I hope Jenna survives a while, because she brings something to the table that none of the main 5 do: A complete unfamiliarity with this particular vampire mythos. She's the only character we've seen actually question things like "where do the clothes go," and, while I wouldn't have my cheesey cloaked bloodsuckers change form any other way I love that it bugs her. Apparently it bugs her enough that she can't even let her mind go enough to transform properly. She can, however, do to her low popularity, quite easily imagine being invisible. And, yes, "Buffy" did it first, but BtVS was basically the golden-era Simpsons of monster shows, so I'm not gonna lose any sleep over that one.
The other vampires are what they are. I love them, but I don't think we're going to see any of them suddenly gain a bunch of new powers or go through much personality change. Gizmo is going through a lot personally, but he's either going to stay a human (most likely) or become a vampire who is way too genre-savvy to play in the Staten Island leagues for any amount of time. Jenna, however, stands to level up right in front of us, and I not only enjoy monstrous origin stories but also the exasperation that she will bring to the others with her learning process. Granted, Nadja has a soft spot for her because she remembers being the village wallflower herself, but I think Laszlo is about ready to see her fly away by now. And Gizmo is not happy with random catering leftovers being promoted ahead of him on the food chain!