Isn't it surprising we never saw him on any show again?

Do you mean Steve Kampmann, the actor who played Kirk? I've seen him in a couple of films since his two seasons on Newhart (For the Boys and Analyze That), but I think he is mainly a writer / director / producer who's done a little acting.

Kampman has kinda droped off the face of Hollywood as far as I can tell. I have looked him up various times on IMDB.com and saw little. I think he was also in a Robin williams film "Club Med?" and in the Michel Keton film "Multiplicity".

By far the best one of the whole bunch in Newhart in my opinion