Hey, one of the devs here. Thanks for trying out our game ^^ really glad you liked it!
Thanks for the help in reporting the bugs also, we'll look into those.
The upgrades do alternate between weapon and stat upgrades so that's why you were only getting rewards every other level after filling up the planet, we want to change that in future versions to make it feel better.
This game was made as an entry for a Game Jam so we had limited time but we definitely want to keep updating, adding more variety and improvements in general.
Thanks again for the feedback! :-)