Originally Posted by gigaplex

For driveability, I'd consider some kind of oil damper. The Pro comes with some clear plastic ones which work okay, but are a little fragile. Either get some TRF dampers (any of 54000, 42273, 42291), or CVA super mini shocks (50746). Also get some suitable springs if you're not getting the TRF shocks (53333 or equivalent). If you're getting the regular kit, get some bearings. I wouldn't worry about spending much more than that, but if you want to go a bit further, look into the aluminium steering bellcrank upgrades and maybe aluminium knuckles for durability.

Tires will make the biggest difference for driveability. What kind of surface are you likely to be driving on? I don't have much experience with tire recommendations but someone should be able to help out there. The kit Tamiya tires aren't very good and don't last long.

For a servo, the Savox 1251 is pretty popular, but even that is probably a bit more than you need in a mini. I'm using a crappy old Futaba S3003 in my M03 and it works fine.