Strangely enough, I have seen a game try this before. You may be interested in "Bloody Rally Show" where you run over the spectators to get a boost.
The trick to this game is to try to stay on the road as much as possible because it gives you just enough acceleration to chain kills in quick succession. If you need just a little more to keep going, you can off road a little bit for a pickoff, but that won't keep your car's bloodlust sated.
My big problem is how it controls, but it requires a little bit of top-down racing skill, which I don't have. This one is competently made, but I do think there's a slight rebalancing in order for something like this.