It sounds like you are out thinking yourself a little bit here. It seems highly unlikely that this villain knows anything about blockers or is even thinking that hard about what your range looks like. He just sees that he has a decent pair.

If you don't have much of a read on him then you won't really know what he'll do with underpairs to the Ace, so I think sticking with a reasonable value/bluff frequency on the river is the right play. If you think you have 3 value combos on the river then you probably pick 1 combo to bluff with. If you have a read to suggest he will fold the underpairs, you can bluff more. If you have a read that says he won't, then you probably don't bluff at all. I think it matters much more how much value you have in your ACTUAL range than your repped range since the villain would have to be able to hand read to understand what you're repping.

Right play. Bad result.

Liked the turn check back and bluffing river. MP just played the hand badly. Raising utg flop cbet in a 3way pot with 99.is terrible. River call he made is a bad call in the long run.

So when he raises flop cbet, his range is a very good made hand, a draw, or sometimes crap. 99 would not be in his perceived range. When he checks turn and river, I would think he doesn't often have a made hand. If he had a set or two pair, he would likely lead turn with two spades on board or bet river after check check on turn.

At the river, Q high is obviously one of the worst hands you could have and villain likely doesn't have a good enough hand to profitably call, so I like the bluff. When you cold call on the flop, you have a pretty strong range. He only beats spades and probably puts you on spades since you didn't bet turn.