Reducing reflections is probably the best thing you can do to increase ANSI contrast when using an overhead projector. I think it is worth the effort, as ANSI contrast gives the image increased depth and that 3D'ish "pop" that you hear referenced. It isn't until you actually see it that the terms become visual and understandable. Once you see it, then you crave it.
Considering all that, I went through the same thought process as you Charles. For my living area system, I went with a real shiny piano black. But I don't care about reflections in this room. For the HT, I do not want reflections or bright stained speakers. When you have a light controlled room with dark, non-reflective paint, everything that isn't like colored will stand out like a sore thumb when you use a projector. But - when the lights are on, even when dim, it is nice to see a real wood, nice looking speaker. When the lights are off, who cares?? You can't (or shouldn't) see the speakers anyway. If you don't care what they look like, lights off or on, then the good ol' flat black with black grill is the best choice.
You obviously do care, and so do I. For a compromise, I decided to go with cherry, bordeaux stain, semi-gloss finish, black grill. They look nice when you can see them, this color matches my HT wall paint (which is a satin burgundy), but when the lights are off, they do not reflect too bad. They do reflect some, but it is not distracting.
