The way it "should" work is like this:
First and foremost, sunlight should always kill you no matter what.
When you drink blood, you should instantly become as powerful of a vampire as you can be, as drinking blood is the token life giver of a vampire. In this mode, sunlight should harm you less (but still kill you if you stay in it for more than a minute or so), and you should look more human, since you would be healthier as a result of freshly rejuvenating yourself.
The longer you go without feeding, the weaker and uglier you become, and the faster you will die in sunlight as a result of being weaker.
This is your reason for needing to feed. This is what it is to be a vampire.
Make it so you can't feed while completely rejuvenated to prevent people from constantly feeding to keep all of their power maxed. They will have to wait until they are drained at least 1 level to feed, and then have to find someone to feed on. That would make deep dungeons with very few humans a great challenge. By the end, that companion of yours might start to look mighty tasty. As it should.
Also make it so that fast travel always lands you there at night. I would presume that my vampire is capable of traveling and hiding from the sun on his way there, and ensuring that he is not standing in broad daylight when he arrives.
As it is now, starving yourself of the very thing that defines you as a vampire is what makes you more powerful. It just doesn't make sense.
Anyway, that's my 2 cents. Not that it's going to change anything heh.



