Ctuna gave you the best advice if your imperative is to get your current car modded.
However, the short answer is this: ultimately, if financials will allow you to, the 335 is objectively the better car to trade into than any mods you could possibly put on your 328. I have a 328 myself and although the AA tune (you'll find it in the boards) was nice, and maybe an exhaust can slightly improve the sound, you will not see substantial gains.
It will come down to what your objective is for your vehicle and how much you want to spend and whether the mods are mechanical or cosmetic. Good luck. I wish more than anything I could personally get into a 335 but I am blessed that at 22 can pay for a car as nice as the one I have without having to eat ramen every night and avoid debt collectors.
As repeated on this forum incessantly, "It's a BMW, no matter what, you'll enjoy it"