I think for Dr. Frankenstein, Matthew would be an excellent choice. But can't you just see Raul devouring this roll?
I don't know if he'd take second fiddle anymore but Raul would also make an excellent Eyegore.
I could also see Tom Hewitt as a possible successor for Broderick as the Doctor.
Brad Garret is perfect casting for The Monster. And I'm surprised it hasn't been mentioned but, Elaine Stritch for Frau! Come on it would be hilarious, I don't care how old she is! Debra Monk would also be great in that roll.
I got rid of my teeth at a young age because... I'm straight. Teeth are for gay people. That's why fairies come and get them