I think the cars have identity already. Balancing of vehicle handling is still in a pretty early state, and I think the way they "feel" along with their visual identity will be all they need.
GRIP strives to be a fairly competitive racing game, which means balance is very important. Giving cars unique "Abilities" like full air control or a third pickup slot can REALLY tip the delicate balance. At best it gives the cars more of a "Theme" and compels players to drive certain cars for certain tracks or race styles. At worst it creates an incredibly complex balancing task for development and ultimately leads to constant "flavor of the month" cars, with the flavor being whichever car got buffed the most in the last point release, which means everyone that wants to be competitive will be driving the same car. Not much "identity" in that situation.
Rollcage had it right with car balance. There typically wasn't a "Best" to drive (Excluding Yuri of course.). Depending on your driving style, your strengths and weaknesses as a driver, or what kind of approach you wanted to take in the race would determine which car you drive. I'm already seeing this in the multiplayer games right now. Alot of people like to be quick and agile and drive the Cyclone, but a few people like the raw speed of the Dreadnought, even if it means stumbling a little when the race throws off your flow. I've been enjoying the Dominator for its balance between the two, and despite some claims that it's not fast enough to justify it's handling inferiority to the Cyclone, It's still just a tad faster, and if I keep a clean racing line, I reap the benefit big time. I haven't seen any particular trend for one of these cars dominating the competition either. It seems entirely up to the driver's style and occasionally the layout of the track. This is EXACTLY the kind of balance I want to see in GRIP. Your choice of car reflects your driving style, not a special perk that you need to utilize for a specific situation.
So, shortly- I think that the cars should all PLAY the same, but FEEL different. I say no to game mechanic perks exclusive to certain cars.