Not to rain on your parade, but I think from an investment point-of-view you should stick with what you currently own and be done with it. Every time you are buying and/or selling a car, you are losing money. Whether it is in depreciation or from mods, people are typically losing thousands of dollars when they buy or sell a car. IIRC, you are 20 years old and soon enough you will want to move out and get your own place. Moving into an apartment is not an investment because you will see no return on it once you move out, so the better way to go is buying a condo/townhouse/house/etc. Chicago is not a cheap place to live and a mortgage is very expensive and even more expensive when you put little or no money down. From there, you have to buy furniture, food, etc., and pay utilities, property taxes, etc. too. All-in-all, the money you are putting into your car(s) is just money you are basically throwing away instead of saving/investing for the future. I'm not saying don't mod or don't buy a new(er) car, but wait until your salary is greater and you have increased income to do such things.
I'm 23, make good money for my first year in the corporate world, and my GTP has 79k on it. Every time I see a GTO/GXP I want to buy one. However, either car will cost 18-25k giving me a $400+ monthly car payment for 4-5 years. By choosing to keep my GTP (which is in realtively good shape), I am saving that car payment every month (plus more) and investing it in mutual funds or an online savings account making 4.5% interest. I only have a few thousand dollars invested thus far, but in about seven months time I've made almost $500 on my initial investment for just letting the money sit. I know that is not a lot, but give it another 1.5-2 years with me increasing my investment at about 1k per month and that amount will grow. Mutual funds can be risky, but generally if you let your money sit you will earn a 10% return or so.
I still plan on modding my car a bit, but it will be sparingly, so that it does not hamper my townhouse fund. I plan on buying a townhouse in roughly 2 years (in the 190-210k range) and putting at least 10% down in addition to having extra money to cover food, furniture, bills, etc.
I guess my advice is to simply look a few years into the future as you will be out of college before you know it. It never hurts to look into the future and wait to do things until you are more financially secure. The same thing goes with your 401(k), start contributing ASAP. Your employer's matching contribution is FREE money!
Good luck with whatever you do... and I look forward to seeing whatever sweet-ass ride(s) you have in the spring.