Nicki and Vicki are without a doubt... dumb. But I'm not holding it against them because they're hilarious and quite self-aware that they're not the sharpest knives in the drawer.
It's that self-awareness that makes all the difference. They're not trying to prove that they're smarter than they are like some past contestants (miss Carolina) and they don't live in a la-la land and get ticked off at the other partner when they make a dumb mistake.
So, dumb but harmless, and FUNNY! I love it.