Some of the home improvement shows on TV have featured either gloss or
semi-gloss white ceilings in homes. They say that it increases the
illusion of ceiling height. I like the idea, but my ceilings are
plaster, and have a lot of "character" (which some might call
"imperfections".)

Would a gloss or semi-gloss paint call out these imperfections and
magnify them? Would it be a mistake to use anything other than flat
paint?