I would think that particles could work very well for this. Also the replicator would make it pretty easy to scatter a multitude of "star" objects, possibly lit with anything glows across a black or nebula background. DCG sells a plug-in for making starry backgrounds. Of course, the way you first mentioned would work well too, using backgrounds made in another program such as Universe Image Creator and PS. A lot of it depends on the POV of your shot and your "camera movement".

Hmmm, you've got me thinking. I haven't tried to do a deep space scene in Carrara yet, but there's a heck of a lot of great tools such as; volumetric clouds for nebulas and gas clouds, several kinds of flares for background star lights and spaceship engines. Maybe I'll try something too.;-)