I'm underplaying it on purpose in these situations because I want the PFR to think he's ahead and spend 2 streets betting at me before he figures out he isn't.
"Value calling" with AK against AQ on an Axx board doesn't happen often enough to make underplaying AK profitable IMO.

I think this is a lot more profitable than throwing in a raise that will only get called by better hands.
I don't think this is true at all, particularly in a loose game. There are only two better hands than AK.

But then again, I'm not in love w/ AK; I definitely don't think its the 3rd best hand in hold'em. I'm behind to any pocket pair and good players can take advantage of this, and I generally only expect to get called by pocket pairs.
Sure, pocket pairs are ahead of AK. However, they are not even nearly as playable and versatile. With proper postflop aggression and prudent laydown ability, a player with AK can grind out a good profit against a player with 99-QQ. If someone raises with QQ and gets reraised (from a player with a large perceived reraising range like me) by my AK, and the flop is Kxx, against most players I will be able to extract a bet or two out of him on the flop and turn. Sure, on an A high flop it becomes a little easier to lay queens down, but even then a flop bet will often get paid off.

I think you are getting a bit hung up on the fact that pocket pairs are a slight favorite over AK. This is such a trivial detail IMO because with any amount of dead money, 47/53 is a profitable proposition. Combine that with the additional postflop playability of AK compared to medium pairs, and the money's in AK's favor.