I'm gonna jump in with a few comments. I don't mind the KTs limp in MP with at least one limper in front of you as long as the table is fairly passive. In the example you gave, I would have called the 3-bet on the flop and then lead out on the turn, especially if no heart appeared. If a heart did show up on the turn, I would probably still lead out. If I was raised on the turn, I'd probably call down.
If I was on the button with ATs with limpers in front of me, I would definitely raise and hope that the SB and BB called my raise. If I had unsuited AT in that same spot, I'd either limp in or fold, with folding probably being the preferred play. If it was only one limper in front of me, I'd probably raise AT to try to get it heads up.
As far as suited hands like QJ and JT, those are definitely playable in EP if the table is loose and passive. If there are many people seeing the flop without raises, those hands should be profitable from any position.
Ben