I fucking love my 328. I've had it for 4 years now, and I dont' regret it at all.
In its 5 years, it's had ZERO problems that required overnight repairs. A total of TWO problems ever, both of which were fixed within hours. I know a lot of 335 guys and I can safely say that all of them have spent many days if not weeks at the dealership or at indie shops waiting for repair after repair. Diagnosing problems every couple of weeks, replacing a bunch of expensive ass parts, etc. My ENTIRE cost of maintenance has been $670 in 4 years (excluding tires that I voluntarily change out since I swap wheels a lot).
If I had a 335, I can guarantee I'd be another $15k into it just to be faster for 3 seconds at a time on the highway. My cosmetically modded 328 outshines countless go-fast 335's simply because all their money is dumped into downpipes, tunes, intakes, blah blah blah blah blah. And yeah, the 328 handles just as well.
The 335 is one of BMW's greats, but it's not for everyone. I wouldn't trade up to a 335 unless my 328 is wrecked and I can't financially support skipping the N54/N55 altogether.