Count me in the "loving this game" camp, but I also have a few suggestions to throw in...
Mostly, I'd love to see some sort of territory system, or maybe just beef up the defensive capabilities of an individual asteroid. As-is, I can have an asteroid with a full six trees, 100+ seedlings, and even with a force that size, the AI only needs to take out a single tree and get maybe 10 seedlings into the core to take the planet over. Now not only have I lost a good source of production, but if I want to retake it, I've got to sacrifice enough seedlings to take over the core, plus another 50 to plant the additional five trees again. Perhaps make it so that the asteroid can't be captured until all trees are destroyed, giving trees more value than just production.
The whole idea of "territory" comes from the fact that aside from one playthrough of the game, every attempt has come down to huge swarms of AI fighters floating around the map and swarming all over my territories as soon as I move enough ships off it to take it over. I can't order the ships back until they get where they're going, so I have to pull them from surroundnig territories, leaving them exposed. So, when the attackers see the cavalry coming to them, they always take off running and end up capturing at least one or two of the asteroids that the other ships came from. And since it takes far fewer attackers to take over an asteroid than it does to re-establish one, I end up slowly losing ships at best, or in a long, drawn-out stalemate at worst. I was thinking that maybe some sort of bonus for adjacent asteroids would be useful to help with this: You could capture any asteroid at any time, but having adjacent ones to the one you're capturing will make it easier (less ships to take the core or something). This way an enemy could still attempt a risky attack into the heart of your turf if they wanted, but they wouldn't be able to completely steamroll your defenders as easily as they can now. Similarly, this could also be helped by making ships orbiting asteroids attack passing enemies. You could then just stack certain asteroids with ships to defend certain areas.
Trees: It'd be nice to have a list of the current tree status on a given asteroid on the prompt on the lower right (the one with the "plant" button). As-is, if I'm rebuilding an asteroid that just got attacked, I have no idea how many trees it has without either zooming way in or mousing over the asteroid itself. On a related note, I think my most wanted feature is some sort of "always on" indicator of how many trees an asteroid has. You can get a good feel for the number of ships orbiting an asteroid by the density of dots surrounding it, but when I'm controlling half the map and just had ten random asteroids attacked, I hate having to mouse over every single one to make sure that they're all at 6/6.