Kim and Shego have a huge amount of grudging respect for each other, though, and have each sought out the other for assistance under the proper circumstances.
Shego/Drakken just doesn't make sense to me, though. I think that through most of the show, Shego sees him as at best some sort of deranged goofball that pays just well enough that she doesn't need to actually do much in the way of hard work. Also, I suspect that she enjoys the fact that he's found so easily by people capable of giving her an actual challenge to fight--Kim foremost among them. The difference is that where Kim sees Ron's bumbling as a grounding quality in her life, Shego sees Drakken's only as a restraint to bigger and better things.
And yes, Ron Stoppable is the ultimate badass when motivated. If they ever decided to truly continue the series, step one would be to make him more capable in a fight and see the sparks fly as Kim starts to wonder if she's being outclassed.