Really fun concept, played it with my friends and we all had a blast exploding the enemies by luring them in the bombs. Upgrading the engine for the first time and seeing how fast we were going also gave us a laugh.
Only thing would be to maybe decrease the value of the green currency to make the game continue a little longer, because as soon as we got to the blue area it was very easy to quickly acquire enough gold to max out on all the power-ups. Harder enemies in the blue zone would also be great, and more zones... but we understand you had limited time because it's a jam.
If the game jam allows it, maybe continue working on the game! It's genuinely a lot of fun, and I'm sure you could find plenty of ways to add stuff (more enemies, more power-ups, zones, environmental obstacles, etc.), we would love to keep playtesting it if you want.
Great submission, well done.