I find that the balancing is actually pretty reasonable, the only thing I can say that is desperately needed to keep up with the amount of time you have to reduce to upgrade a car is by using every 25 levels or so on a car to increase the amount of money it gives etc.
This is actually done in the dev version. We are playtesting some balances to the numbers, and should have an update out in about 20 minutes or so. Thanks for playing! EDIT: Took a lot longer than 20 minutes,due some other necessary changes, but...Fixed!
1.00 is the 2%