Thanks for giving it try!
I'll have to look into the driving issues you had, by change directions, you mean as you steer left and right?
When you kill an enemy, they have a chance of dropping a gem. Pick up enough gems and you will level up and be presented with three options to improve yourself, but each has a downside as well (the KEVIN aspect). The gems aren't as visually attention grabbing as they perhaps should be, but it's a balance to not have them be distracting. A balance I didn't have as much time to play around with as I would have liked!
Edit: Added a screenshot of the upgrade screen!