Didn't Robert sort of bankrupt the Crown? I see your point and sort of agree but I like to think that Varys took a look at Joffrey and thought "No fucking way we're dealing with this for the next 40 years. Let's try the other crazy guy" :)

IIRC Both the wolf and the Sand Snake girl are named after the original Nymeria a legendary warrior queen, not one for another. But yeah SandSnakes are the worst.