Since the post asked for opinions of cross-breeding, allow me. My opinion is that cross breeding should be done to achieve a worthwhile goal.
For some, that means coloration/plumage, or some variant of that. Done mostly for show, to look pretty/different, or just to experiment or to prove you can do it, I say sure, why not? Such experimentation has surely led to serendipitous accidents in the past and you might develop the next "fad breed."
Sometimes there is a payoff in hybrid vigor, too, and that seems a worthy offshoot. But it doesn't appear in all crosses and doesn't breed true later. For the backyarder trying to maintain and even invigorate a flock, it is a dimishing return that is better left to hatcheries. Pure breeds true and the good qualities remain, so I say stick to them when breeding.
Since meat birds have about reached their peak in the Cornish crosses, I see little reason to expend effort and money along that line. Capons are another matter, but they are a specialty and not cross-bred at all, so dont really apply here.
But, there is one area where anyone can make meaningful, measurable improvements and that is with egg production. It is my opinion that there is no higher goal in breeding chickens than excellent egg production. IMHO, that is what you should cross breed for. Things like pretty feathers or goofy necks should take secondary status.
