It's far more interesting to have a cured Barnabas than a vampiric one, because that's what set the tone for DS as a unique, original, compelling program: the totally unexpected medical treatment, instead of priests and whoever running around with stakes and battling against "evil", a redeemed vampire as the (?!) hero. Horror movie makers don't get the need for some sort of hopeful element to the story, to balance out all the gore.
But what's even more important is the need for change, sometimes radical, horrifying changes in the story and in the characters' lives. There has to be the risk that BC will have his new life taken away, and for the risk to be credible, it has to happen once or twice.
For me, the value in BC being made a vampire again in the Leviathans storyline is not that it's somehow better or more "enjoyable" in some way to see him as a vampire. It's not. (And it's not as if we DO see him as a vampire really, if he's not showing any signs of it, never feeding.) The value of it is that it's a tragic outcome for Barnabas. It's great for dramatic reasons. I hate to see him LEFT as a vampire for long periods, though.
I don't like to be judgmental like this, but respectfully, JF really had no business turning his nose up at the core activity involved in being a vampire, the part he was there to play. Maybe they wanted to just leave him that way indefinitely though, and then I'd have had a serious problem with it. Maybe biting meant big ratings. He'd become a monster, possibly, and the drama would suffer. Come to think of it, that must have been his concern. So maybe he thought, fine, I'll let them make me a vampire again (DC et al), but without feeding, so we get the drama of it, without the gimmicky stuff some of the less thoughtful kids would be tuning in for.
Mr. Frid is winning me over without even being here.