You know, you bring up two interesting points. First, making Hans a full-time castmember. I like that idea - he'd make a great foil for Marguerite. He would probably contribute more in the story lines than Ned certainly does (the only thing he contributes is his pining for his unrequited love in England and a potential romance for Veronica). Theoretically, both Roxton and Ned are expendable. Hans could become Marguerite's foil (currently done by Roxton) and Challenger could assume Roxton's position of deep jungle explorer, coupled with a strong scientific background.

Second, as for a recurring nemesis, my vote still goes for the saurian empire of lizard-Romans. Certainly a more capable foe with deeper resources. And they know how to show a gladiator a good time. :)

As for the other evil dudes you mentioned, a good hoot if Landis wants to play up the campiness of the show, but I think Doyle would turn over in his grave (if he isn't already).

Enjoy!