Well, Stargate is well into Season 7 -- or is it 8? -- with talk about another season *and* a spin-off... but that's always been a very plot-based show.
A character-driven show like L&C depends on the characters facing challenges -- the "will they, won't they" sexual tension stuff is the most common kind, and apparently the kind that Hollywood writers really prefer to write.
Umm... hadn't really meant for this to get so long!
You've just touched on one of my pet peeves -- of all the standard plot devices above, the "sexual tension" one seems the most popular, with the most potential for infinite repetition. And some people do enjoy that, but I have a limited tolerance. If the third season hadn't begun with a revelation and quickly segued into romance, I probably would have quit watching.
PJ