Yipes,previous post sent in error in unfinished state. And no, it wasn't a deliberate ploy to increase the number of posts :-)
In the Stargate case, I'm watching more for the actor than the character, though the character is fun. The only series where I actively prefer occasional characters to the regulars would be Xena and Hercules, especially Hercules. Autolycus and Ares are guaranteed to liven up any episode - I'm also fond of Aphrodite. But then I prefer the humorous eps of those series to the serious ones. I probably wouldn't watch the series if I didn't like the regular cast at all, but then I wouldn't have got as far as the eps where the fun guys first showed up, would I? So it's probably a self-fulfilling thingie that fans don't watch a series purely for the occasional cast.
Louise