In my slight experience, bigger-background PCs are better for lower-mortality games; smaller-background PCs are better for higher-mortality games. Folks who've put a lot of work into a PC are going to play more cautiously, generally, because they don't want to see all their work go down the tubes.
Also IME, the bigger-background players are often the same players who don't have a great handle on the rules: they focus more on the story, and so their PCs aren't as likely to be optimized.
One thing I've been thinking about doing is issuing Hero points to folks who put lots of work into the background and into campaign maintenance (writing journals, coming up with cultural fluff, creating new NPCs, etc.) A Hero Point would be good for escaping death (stabilizing the PC at -9 hp) or for attempting a dramatic action (lassoing the roc as it flies away and climbing up the lasso to attack it).
I like this idea better than giving out character-generation points b/c I think it meshes better with the high-background playstyle.
Daniel