Yeah, I'm not sure what causes that issue with the getting stuck on walls, I've had it before. I'm just using Unity's built in physics and velocity, so it's as if there's 100% friction when moving towards a wall, even though I assigned a physics material with 0 friction. Yeah, I probably could have created some effect for getting hurt, but for enemies spawning I feel that after a few minutes so many spawn it'd be too much.
Powerups is a neat idea. Maybe increased max health, reduced attack cost or energy regain, larger area of effect, etc, there's good potential there.