Whether you gain or not by curing Serana ia totally irrelevant. The question concerned how to do it and the ticksy tricksy "it's too late you asked the wrong question" 250 hours of play-time ago is not amusing. If you are not playing a vampire character then there are certain things you want from a follower. To begin with, all followers should have a uniformity since many players run with more than one follower.
I return to my home, tell my followers to relax, and I get some sleep. Unfortunately, none of the multi-follower mods know what to do with with Serana because the source files have not been released. So, I have to give commands to my group and commands to Serana. Being a nice guy I am stuck to staying out of the sunlight, sleeping during the day and watching all my followers go off to bed but not Serana. I have a home with a coffin in the cellar but she doesn't use it.
I only have a quarter of the commands of those I have with the rest of my followers with her and if I wanted a vampire I would have played one myself. What I have is a lame duck follower and I'm not impressed.