You start out with 0 exp. That's pants-on-the-ground retarded. I was REALLY close to leveling up at the end of stage 1, now I'm on stage 2 with 0 exp and getting pwned.
The towers need to target by distance from the exit. I just lost at wave 500 with 4 mega-mega towers boosted by 4 mega damage/reload towers because they kept shooting at stuff only halfway through the map rather than the level 500 ghost bosses about to lose me the level.
My ships are kicking total ass in Blender, but the planet's strength never goes down... It also reported about 6 habitats being built there, but I never saw them no matter how hard I looked...