Thanks for the compliments and triple thanks for the critical feedback :)
Difficulty is definitely something that needs work. I'm trying to balance for both experienced gamers and my kids (2 of my helpers on this project). There needs to be a difficulty curve that starts low but goes up more dramatically over time. The rate is currently a bit slow.
Right now, as the game goes on there are more astroids in play at any one time, so that's supposed to make it more difficult. The reality is, I think, the opposite, where the additional astroids are causing collisions with other astroids so there are fewer crossing the play area. I think your suggestion of making them faster (and maybe smaller) might add some difficulty to it. Asteroids that split into multiple smaller astroids on collision is worth considering as well.
Rewards are something I was hoping for, but didn't quite get in scope in time. Increased capacity (slots and per slot), faster ship, proactive shields, and automovers were all cut for time. Adding them would give more incentive to collect resources and lead to a more proactive game experience. Should be more to spend credits on than just reactive repairs.