"Is asking for a writing partner more trouble than it's worth?"
Depends on who responds. And if he or she is trouble.
"Legally, when it comes to quibbling over percentages of who contributed how much to a story or project and what they get paid or reap in royalties, is it worth it or not?"
I've never done it, but it would seem like a fairly simple proposition to write up a document that says "Each of us does half the work and each of us gets half the credit and half the rewards, if any." (Or whatever you agree to.) Or have a lawyer do the same thing.
"Is someone who wants to do it all on their own considered stubborn, or greedy, or maybe even lazy?"
Didn't see that one coming. Lazy? I guess someone who wants to do it all on their own, but doesn't do anything could be considered lazy. But you probably wouldn't want a lazy partner anyway. If I buy a lawn mower and go door-to-door charging people to mow their lawn, and don't get a partner, does that necessarily make me greedy or stubborn? I wouldn't think so. Some people might even call that ambitious.
Paulo Joe Jingy
Sometimes some things just ain't right.