Also
Comparing the functionality of both cars isn't very fair at all.
But isnt that what this is all about?
A tricked out Ferrari wouldnt do any of the stunts the Tumbler does. Sure, if i was making a comic book and my hero would have a car, i would give him a nice supercar with rockets and gadgets. I wouldnt even think about a tank because i think that they are ugly and impractical in a city.
Nolan brought a new idea on the table. Its not exactly a tank (in the military or DKR sense) and its not exactly a car.
Granted, it could look a bit more beautiful, but its all kinds of stealth fighter badass! The uncovered wheels are its only weakness i can think of, while its jumping capability is a great asset. Both practical and awesome! Just look at this scene from TDK where it jumps over a car. It doesnt only jump across rooftops.
On the other hand, you could have a supercar batmobile with repulsors under it that would fire for a second to allow it to jump. Plot hax would cover the rest.
Also, some people argue that batman needs a real stealth car. A car that will pass unnoticed. Well, a tricked out supercar isnt a choice then. A Ford maybe? And you ll have a superhero drive in a Ford? I'd rather have the unrealistic route.
For example the BTAS-mobile had some sort of plates coming out of it that enclosed it and made it look like a dumpster.
"Much more subtle"
After all this though, i gotta say, i cant see Batman going back to the supercar type. I got used to the tumbler and it looks a lot grittier if you ask me.
EDIT: Remember those batmobiles in the comics that had a giant bat face as their grille. Jesus Christ who had this "bright" idea?