Isolating on limpers is very profitable, and if you are tossing hands like KTs on the BU with 1-2 limpers, then yes you are losing out on some $$$. Hands like Broadways and decent aces are great to isolate on limpers from LP. Likely you are already ahead of their range. You will have position which will allow you to easily either valuetown them when you hit, or pot control when you feel weak.

Hands like suited connectors, small-mid pps, probably perform better to just limp behind others in this situation. With these kind of hands, take 55 for instance, you aren't going to hit the flop hard often enough. THe only flops you are going to feel really comfortable on is if you flop your set. So if you isolate with a hand like 55 on a limper, and he calls, and you miss the flop and he check/calls your cbet, you have very little equity or SD value in most cases.

Also, remember just like everything else in poker it depends on the villains. Villains that like to limp/call, and have a high fold to cbet are ideal to isolate on. They are the type that believes any two cards is profitable to play until you see the flop at least. And they likely play fit/fold postflop. So raise them up, take the flop, and then take the pot. Ez game.