Thanks a lot for trying out my "game" and giving me some comments.
The parallax effect has 6 moving layers and one static background that moves with the camera. I have adapted the parallax effect script from here to basically take a list of layers and animate them based on the number of layers you give to it.
Yes getting inside of the asteroid before it blows up is the most effective way of getting all at the moment. But that will not work when the collision is in :-)
For the movement, I think I have to see how I can adjust it. I like the concept of turning and accelerating/decelerating, but at the moment it feels too sluggish, I see that. It works quite well when you have some movement speed and I like to zoom around, but esp; when you have no speed build-up yet, it feels too slow. One option is to just make it faster, the other is to put it in the "upgrade system" to get better engines. I tend to favor the latter one.
For the asteroid spawning, I use a uniform Poisson disk sampler. It is based on the one from this article, which I adjusted to unity. It works quite well.