I've always thought the closed/capped looked great on the E34 (like Anita's B10 BiTurbo), but a little wrong for the E28. They look good, but don't blend for me like the open wheels do.
I vote for closed lug, but it's a really close call. I don't think the "period correct" argument should have anything to do with it, and the the closed lug design just looks cleaner to me.
I guess you better keep both sets, Roy, and just bolt on the other set every few times you drive it. You'll never second guess your decision that way.
One day, I hope to be in the position to have to make this type of decision. Right now the kind of decisions I make are more along the lines of: Fix the truck or the BMW or the Honda. I can never do more than 1 at a time.