Priorities, man. Put your pennies in the bank for college. You'll never make your money back putting goodies on your car. In fact, you'll probably decrease the resale value and possibly affect the reliability when you need it most.

I would have to agree with 155927 about saving your cash and not dumping it down the bottomless pit that we call an automobile, but maybe your parents are loaded and you can blow every dime you make without having to worry about paying for college, etc. Without knowing more about your finances it's hard for us to give relevant advice in this area.
With that said; the easiest and least problematic way to soup up a '00 323i is to trade it for a '00 330i with the Sport package. Plus, any upgrades you do to the 330i will give you more bang for the same buck.
Personally, I like what Brian suggested if you are bound and determined to catch the disease, I mean, enter the wonderful world, of car modification: trade down to a good e30. You would not believe the amount of aftermarket goodies out there for these cars. You also reap the added benefit of a much greater availability of knowledge. Because these cars have been around for so long everything has been done to them, and you can draw on someone else's experience. In my opinion, this is the best tuner car you could buy. Lastly, and this is purely subjective, my e30 is more just plain "fun to drive" than any car I've ever owned, including other BMW's. Good luck.

Well Evan, since it's been 27 years since I was your age and considering the differences between then and now (both in personal perspective and just the world in general....)

I'd start with the bit about where your friend's cars 'are' (wherever that is) relative to yours, and suggest considering why that's where you say you want to be. In other words, make sure that what you want to do with your car isn't just for status or peer pressure, but because that's the choice you really want to make for how to be spending your earned dollars.

You don't really specify what you want to do with your car. I can't speak for the specifics of your model, but generally, there are virtually endless varieties of modifications available for BMW's, as you've presumably noticed from Roundel and other magazine/web/etc. advertisers. Whatever you want, there's probably somebody out there doing it if you can pay for it. So, as for souping it up, as you say, I imagine the stuff is out there - now, as to how affordably or easily mechanically achievable mods are, depends on whatever it is.

I do have to concur with some of the other replies - remember to consider cars objectively (at least as best you can, if you're a car nut sometimes that's less easy to do, but I digress..) - from an investment standpoint, cars NEVER appreciate in value, they only become worth less and less. So, any money you spend on a car is not really an investment in the car. In reality, it's for some other reason (maintenance, prolonging it's usefulness, changing/adding performance/functionality, etc.) - investments (hopefully) yield a monetary return in addition to the initial money invested, and what you receive from spending money on a car is typically less tangible, and in most cases, you'll never get more money than you spent for anything you do to a car (expect to get less, actually, sometimes substantially less).

I only mention that to put it in perspective - if you want to make money, save and invest intelligently, and some years later, you _should_ have more money than you did initially.

So, after that, then consider your car, whether it's worth changing anything about it, and if so, then what you would want to change, and what your budget is to be - make a plan.

For some additional perspective, do consider that you've got a fairly evolved excellent vehicle to start with. I had a 320i in the 80's, and compared to today's amenities, it was fairly basic transport - manual windows, no power door locks, 105hp, barely adequate a/c, no cruise control, no power mirrors, no traction control or abs brakes (both of which were yearrrs away yet), seats only comfortable for drives of about 1.5 hours unless you had a sponge for a spine, basic radio w/ speakers that sounded just ok at best (hey at least it had a radio and a/c), tendency to snap into oversteer if you dared lift off the throttle at any kind of handling limit, 'exciting' handling in the snow, that is if you could keep from getting stuck in the snow since it didn't (initially) have a limited-slip differential...

Well, you get the idea - comparatively, your 8 yr. old 323i is several worlds of advancement compared to the BMW's of nearly 30 years ago. My 320i cried out for a couple of things just to make it much more useable, a limited-slip diff for winter driving and a Recaro seat for the sake of my back (neither of which, mind you, were much value-added at the end of the car's life, monetarily speaking).

So - mods... that's really taste and preference. If you're talking cosmetic, just so you can look cool, man - I say, why bother, waste of time, there's no performance benefit. My tastes tend towards the functional - if it doesn't make it go, stop, or handle better, (and the less outlandishly or noticeably visible, the better), then I'm like, why bother.

Is it worth it for your car? That's up to you I suppose - you could spend a hundred thousand dollars maxing out your 323, and as the other post mentioned, there will always be something better, faster, etc. out there. That's part of why it's important to do things to your own satisfaction, and keeping to a plan and a budget.

If you ARE considering upping the car's performance envelope, the ONE thing I would strongly suggest before you launch down that path - is improving your OWN driving capabilities before you spend dime one on the car. If you are realistic, you should understand that your limited driving experience so far, no matter what you think you know, does not yet anywhere nearly approach the performance capabilities of your car as it sits now in perfectly stock form at 8 years of age. (Unless you tell me you've been a professional go-kart racer or something like that since you were age 5). I've been attending BMWCCA track driving schools since I was a few years older than you (instructing for years, now), and I can certainly tell you that you'll learn more about driving, driving technique, and car control more quickly at a BMWCCA driving school than anything you'll be doing w/ street driving for a long time (Auto-x is fun too, but I'd say start w/ driving schools to get the basics in place).

If you're willing to do that, I'd say save up your money for that experience (and yes, sadly, you'll have to wait until you're 18)- in the meantime consider getting to a 'CCA foundation teen driver's clinic if there's one going on anywhere near you.

That way, you'll build a skillset that will serve you for your lifetime, and help you not make a stupid choice that turns you into another sad all-too-often statistic.

Case in point- last week here, a 25 yr. old guy (kid?) was driving a Lotus on one of the city streets maybe 1/2 mile from where I live - this is a wide street with a long downhill straight section before it has a couple of broad sweeping turns going into a little business square area. 4 lanes wide, w/ parking on each side, so 6 lanes wide altogether. God knows how fast he got up to, but he lost it and ran into a huge tree and it literally split the car up to the tail-light section. The news clip showed the tree, and about two feet of the tail-section (front-to-back) was up against the tree trunk, and width-wise, that tail piece was the only intact piece. The rest of the car was in pieces all over.

So, as sad as it is, that's a story that obviously has 'stupid' written all over it - stupid choice to drive a car that capable, that fast, on a city street, and without the skills in place to handle that kind of speed. Please don't misunderstand, I'm not saying that if you have the skills, it's an excuse to drive insanely on streets with 35mph speed limits - the point is, if you like to drive, or you like to drive fast, and you like/want/have 'fast' cars, then it only behooves one to get the proper training and save the fast driving for a much safer and more appropriate environment, a racetrack, whether at a club driving, or actual racing, event.

And also - if you happen to like working on your car and learning about mechanical things - get a Bentley manual, and some selective purchases of appropriate tools - plus, if you get into driving (as I and so many other 'CCA track junkies have), you'll be able to do some of the maintenance basics necessary like changing brake pads, fluid, etc.

A couple of other things to note - the average market won't recognize the value of whatever you modify on your car, and as pointed out already, that may de-value it or make it less sale-able for the regular market; enthusiast-oriented mods are only going to be of interest to a like-minded enthusiast market.

Also - although I don't know what you'd say a 'normal' 17 year old spends money on (chicks? booze? drugs? guns? Sociopathic videogames nonstop? Cheetos & Mt. Dew?), I'd say a high level of interest in cars at your age is not particularly unusual for any reason - teen males have been interested in cars and how to modify them since Henry Ford had them rollin' off the first assembly line 100 years ago. Given the gamut of possibilities, I'd say there's a whole lot of worse things to do w/ your money than spending it on your car. Sounds generally like you're hard-working and responsible, so, kudos to you for that @ age 17.

Sorry for the length - hope that helps some -