You could have "locked" library objects. You wouldn't be able to edit them. The great thing would be that you could store just one of them in the memory, and then only the positions, angle and other modifiers of the others.
Oh yeah and finally, of course, wanted to suggest that months ago
Symmetric objects. 1/2, 1/4 symmetric, would be even bigger ease off for the ram. Which brings me to, could we probably have another view for symmetric/library object edit? With levels, hierarchy and such. Like a library of the scene.