The aspects of the vampire that are interesting for the story could be better placed in a non-vampire character (why I suggested a genetically-engineered person like Khan), while still maintaining diversity.

Whereas "vampires" immediately call to mind Vlad, Dracula, Twilight, etc. and an entire literary tradition of the last century, which Blindsight has little to do with. There's the riffing on crucifixes with the right-angle seizures, but that's more cutesy than serious.

It's not the worst decision on Watts' part, but I think you're in the minority in liking it.