On the M3 front, you're missing:
Far better steering feel
Better throttle control and response (mostly due to the NA engine)
Far better seats (larger and adjustable bolsters, way better leather)
EDC (if you get it)
Better brakes (will still definitely need better fluid and probably better pads for track duty)
NO RUN-FLATS!! (and larger tires overall)
Exhaust note is of course subjective, but IMHO the M3 takes the cake because of that V8. Try a rev-match from 4th to 3rd around 70 mph; that throttle blip is virtually silent on the 335, whereas on the M3 it's life-affirming.
But I've said it elsewhere and I'll say it again here: The M3 is definitely a more fun car to drive even on a commute, BUT if driving it on city streets and freeways is ALL you'll be doing, I personally don't think that it's better by an amount that justifies its added cost, both in purchase price and ongoing running costs. If on the other hand you'll be driving on twisty back roads and especially on the track, then the added cost makes perfect sense. People who have never taken their M3s to the track will never grok its real reason for existing. If you get the M3, do yourself a favor and take it there at least enough times to become a good enough driver that you can see what this car is really all about. That of course will add to your M3 upgrade costs, but it's also one of the most fun per dollar experiences available IMHO, and there's no point in getting a more expensive and sporty car to use it the same way you used your previous car. Good luck OP!