Does it pay to mist tom seedlings?

No need for it at all.

Glad I waited before going in gung ho. It's just a bit strange that one minute they look happy as Larry and the next day they look pale and unhappy with their lot.

If you look closely at a tomato leaf you'll see a fine hairiness to them and this would only trap any mist and cause the leaves to rot, which you obviously don't want. Smooth-leaved plants are designed to retain moisture and would gladly absorb leaf moisture - from the underside. Unless your plants are suffering in a drought situation, there's really no need to mist them unless you're doing a foliar feed.