Generally speaking, I can manipulate lure bodies back into molds far easier than their tails with my hotdog fingers... difficulty comes down to the size of the pieces I'm working with.
As long as there is a mold, I definitely use the mold. I only use a flame or heat gun when making "franken-lures" (joining bait parts from dissimilar molds)... my long-standing favorite is a Mogambo copy with the Stump Thumper tail, but I also do this to beef up the crappie fluke... for me, having the specific bait/action is more important than perfect seams.
For selling baits (and personal preference), detailed appearance can be key, but it's largely a non-issue to the fish (or they wouldn't bite most lures tossed their way).