still, even with sensors, it's kinda nice. if you build that level of tech, set up storms in your systems. these negate shields and can have an incredable impact on the AI. just get orgo-tech and a good level of organic armor...
I have created stars inside of a nebula system, and then destroyed the nebula without harming the star.
This could have been a bug. I haven't tried it in a while.
Please note: There is no reason that I know of you could NOT change the data files to add "nebula" systems with planets to the game. It's just a matter of editing the systemtypes and quadranttypes files. Could be very interesting. It certainly adds an extra incentive to develop sensor technology.