Tune'll give you more power, but magnify suspension deficiencies.
If you're looking for a cosmetic redo, maybe I'm not the guy to talk to. FSD's solve the egregious 'pothole explosion' issue afflicting pre-2011 E9x - you'll like that.
LSD puts power to the road in a way that can be felt @ 5 mph, and greatly assists handling.
The rear end of these cars is distant. I'm tellin' ya, money spent on suspension work will flat put a smile on your face, but ain't cheap. Read about M parts, especially sways and rear subframe bushings - here
's a good place. Sooner or later, you'll want this stuff.
Suspension mods also enable existing power to be put down efficiently - you may find you don't want a tune if the suspension's fixed, as tunes can make the car somewhat edgy.
Good thing is, extensive mods available, whatever direction you go.