Hello Jibb!
As I was on vacation I could not test your new version of KarBOOM (and then admittedly forgot about it) but now I've caught up on it.
An honest critique:
I've liked your old version (KarBOOM 0_3b from Oct 2011) better, not because it was still using acknex but because the gameplay is better, the handling of the cars, it's just more fun to me. Please fire up one of your old versions and compare the handling of the cars (tried middleweight and heavy cars), I don't even know what it is, maybe that the cars right now react too directly.
A few more points: Where is the boost-meter? The boost effect and in general the explosions looked better in your old version but maybe this is because of limitations of your Unity edition, I don't know. Adding multiple bots is a little cumbersome right now, maybe you could add a button that adds a (randomized?) bot or remember the "bot" type when I add additional AI cars. Hm I thought I had one more point about the HUD but nevermind.