Ok, so your point basically had nothing to do with mine. Got it.
Had everything to do with your "point".
Klingons haven't been used as much as say, Kirk and Spock, and they still work.
If I may expand and clarify.
Kirk and Spock are the leads, of course they would be used more often than Klingons. Not an apt comparison.
But see, that still has nothing to do with my original point. My point was that just because something has been done a lot doesn't mean it can't still be done again. The frequency with which it has appeared has no bearing on its future appearance.
The people who moan about Klingons appearing are the type that whined about Kirk and Spock being done again. It doesn't matter who the leads are, there are some fixtures that belong to Trek, and the Klingons are definitely one of them. To be upset about it or to start counting how many times someone else has appeared makes no sense.
So what if Khan only appeared twice? Kodos only appeared once! Or someone like Nero had never appeared. Or the Romulans had appeared several times before. It's a ridiculous argument and complaining about it seems petty, especially given the context of these movies being made.