Addicting!
I love it! Played it one first difficulty and won... then played on second and lost rather quickly... then tried again on second and almost lost at the beginning but made a hell of a comeback and ruled the galaxy!
I can't believe this is only a Beta!!! This was perfect as is... but please don't make the full version too complicated. Once you add ship upgrades and different tiers of specialized stars (like Defence lvl 1, lvl 2, etc) then it's impossible to catch back up once you've fallen behind. And you have to be constantly checking the menus and thinking "is it the right time to buy this upgrade? should I buy this or this? Are the upgrades balanced or is there one that will help me out of this particular situation?"
It may seem like a boring idea to you, but I suggest that if you want to add upgrades and tiers, etc, you should make them automatically affect all players depending on game time. As I said before, your game is perfect as is. Adding visual changes periodically throughout the game will make it more visually appealing and will keep people's interest longer. Even if you don't technically have to "work" for the upgrades, they are your reward for simply staying alive.
Honestly, think about it, the only complaint that people have is that it is too hard. Would you want to increase the complexity of the game by forcing people to micromanage? That will only increase the number of complainers. Give them the micromanagement for free but show them the progress, and they will be more interested.