Nice little prototype. I think it's too small to worry about condensing events, & too early for polishing. Instead I think you should experiment with extra game mechanics, here's some ideas that sprang to mind while playing:
-it's kind of an arena shooter without the shooting (arena dodger?) so how about some of the tropes from those games like a countdown to announce the next wave, or indicator to telegraph where they will spawn.
-some kind of powerups: extra maneuverability, speed, shield recharge, bombs, decoys...
-it's an evasive game, so how about scoring based on near misses? if you pass within a certain range of an enemy maybe a power up bar increases.