Current, if a planet is 1000 negative a month that can easily be paid for by prospering colonies somewhere else.
Which is a great opportunity to bring a bit of mass psychology into the picture: people anywhere usually don't like it when they have to pay for "lazy buts" at the other end of the Galaxy. Taxes could be calculated per colony. If too much of the tax money of a colony gets spent improving another colony instead of theirs, there is unrest. You can fight this by making colonies as self-sufficient as possible, financing propaganda programms (making people feel more as a part of a greater whole etc.) and so on. It would be great if it also would bring a more complex taxation system: set taxes for colony level and empire level (after all, regional and national taxes are customary in most states).
Civil industry would certainly be cool. We already have civilian mining and shipping lines, so industry would be a logical next step.
Predictability is boring.
I thought in a strategy game, EVERYTHING is about predictability, i.e. your ability to predict stuff happening and taking adequate steps to prevent it from happening. Randomness might become a very frustrating factor in a strategy game. I'm not saying it has no place at all (there's a LOT of randomness in Aurora, after all), but throwing your economy upside down without giving you any chance to foresee and prevent it might be a tad frustrating.
For example, I had a financial crisis quite lately in my game. I saw it comming for a while, and had the opportunity to catch it by building financial centers and putting all my research into economy +20%. I had to take a lot of resources off from stuff I'd rather had been doing, but the problem had to be solved. And I solved it, just in time (I went something like 120 into minus). If I had a random economic crisis at that moment, I'd have been screwed. Now, if that crisis occured because I missed some important developements and stats, so be it. That's the game. But if that crisis happens purely out of the random generator, without me having any chance to prevent it whatsoever, I might just get a little frustrated.
Economic crisises usually happen because people are shortsighted and greedy. If a player is either, he has plenty of opportunity to get himself into trouble of any sorts, that to him might come quite unpredicted, while an expert player would have seen it comming long ago and took according steps to never even let it get a real problem. That's the fun of the game, at least for me. that, and exploring... I LIKE exploring in Aurora. It's also a pretty random thing, but it's still not so random that you couldn't saveguard against it. You ships don't blow up randomly, they blow up because you designed them badly, or neglected to watch their maintenance clock, or they get blown up because you didn't take neccessary precautions. For the economy, it should be similiar: a certain degree of randomness, ok. But it should still be predictable in a way system failures on ships are predictable.
If anything should be added randomly, then maybe disasters, that can also have an influence on your economy, but are justly random. There's no way to foresee that your major ordonance factory will blow up tomorrow because some bloke decided to have a smoke...