They never really developed the Tooms character in the series, and somehow he is a huge part of XF lore. I like stories that explore previously unexplored avenues. I particularly liked the part where he was laughing at Nosferatu. It makes sense that he would find the consumption of blood weak and trivial compared to his hunger for livers.
Not sure about Scully being undying though. I've always thought Clyde Bruckman was referring to her not dying of cancer. I never been a fan of Tithonus, I just thought the writers were being lazy with that one.