Sorry, just skimmed through the post, (I was on the phone) Doubt they'd get much support or change nationally if they did form their own party, much like the independent party or the Green party. Like it or not the two party system is deeply entrenched in this country.
You know, nationally, it might not be great in the short term, but the blow to the Dem party might be painful enough to at least get the Dems to start taking the blacks seriously other than at voting time. The problem with that is, now that we've got 10's of millions of latinos we didn't need here, Dems don't really need to court the black vote all that much (I mean, are blacks going to vote for Reps? No, so, who else will they vote for? They'll either vote Dem or stay home), so the blacks are sorta now screwed...still somewhat relevant, but not at the forefront.
State and local, I think it would actually be a boon to them. No longer would blacks have to kowtow to the Dems, they'd actually be in charge in some of their locales where they have large majorities. Imagine a Chicago area where instead of having black Pols that are hindered by being Dems, they are under their own party. The Dems can't just do whatever and leave the blacks sold down the river with scraps, they'd actually have to work with the black party to get shit accomplished.