But now that I've finally run into someone else who remembered it (over on mightygodking.com) and told me the title, I can finally understand why someone might suggest Battle Beyond the Stars as a possibility-- Corman reused the sets, props, spaceships, a few space scenes, special effects, and even James Horner's music from Battle Beyond the Stars when he made this piece of B-movie schlock, Space Raiders.
The rest of this post isn't inteded to inflict Corman-sans-Rifftrax on the rest of you (and as an average-quality Corman flick, man oh man does it ever scream out for the MSTie treatment) so much as just put the links somewhere that I'll be able to find them later. In a few years. After I've forgotten the title again.
Feudalism: Serf & Turf