He's one of my lest favorite villains, so one ep was enough for me. But seeing him interact with Spike might have been worth one more episode. It's not like I doubt Joss or another writers could have made him interesting, but I'm still satisfied with what we got.
A villian I wanted more from was The Anointed One. I think he was suppose to be on longer, but the actor grew to fast for the role, so he had to go. I'm not to sad, because then came Spike, Drusilla and Angelus, the most entertaining villians ever.
Sunday from Season 4 was a delight. I would have loe to see her and Spike cook a plan up, so I would have wanted her for at least one more ep.
There's probably more villains I'm not thinking about right now, the writers really knew how to write the creeps well, but I can't remember.
Part of the charm of monsters of the week is that they came, they scared/charmed/made us laugh, then they left when they had done what they were suppose to, before it got old. A few villains stayed too long. Like the trio. One ep of them would have been enough. But they did represent the occasional lameness of life, the need to desperatly grab for something great, so they did fit in with season 6's theme, "Life Is The Big Bad".