Space stage is beginning to pall--- I've tried most of the different strategies but they end up feeling about the same. To engage in a war you need to build up your defense + get cash for weapons. In order to do that, you terraform (better planets == more defense) and trade spice. Same deal if you want to build an economic empire--- you terraform to increase production. Even if your goal is simply to terraform you need to scrape together a fair amount of cash to bootstrap yourself.
Unfortunately, terraforming is simply not all that interesting. You can pick which plants and animals to put down, but there's no challenge to it. In fact, finding the herbivore you want can be downright annoying if the game spawns one of the planet's other inhabitants for most of the herds. A more complex game would extend interest, but there's no skill of any kind being taught as-is.
Sculpting planets is not all that interesting (you can't share your sculpted planet with anybody to brag) and takes too long with the tool recharge times.
Pure exploration is kind of fun but constant crises back home compete for your attention--- you really have to be a Shaman to make this work. I haven't managed to collect a complete set of any of the artifacts. It would be nice to have some way of searching other than brute-force: can't your allies help? Couldn't you pay for information? Send out scouting expeditions?
Interacting with allies is also noninteresting. Even brokering peace agreements might be fun. Having two of your allies demand your help to beat the other one senseless --- not all that fun. You can ask allies to attack, but what about giving them the other sorts of missions they give you? Artifact and organism retrieval, terraforming, exploration... running an empire instead of merely running your ship could be fun.
However, the core 'sandbox' is still enjoyable--- I like putting together creatures, buildings, and vehicles.