Frankly I think it should just be that Ulster democratically decide which country they should be a part of, and that be that. Right now they would continue to be a part of the UK, possibly due to demographic changes they'll choose Ireland later.
Actually...for some reason the electorate decided to jump to the two more extreme parties instead of the UUP and SDLP.
SF's fortunes dipped in the years before Good Friday. The party then did what the voters wanted, and are being rewarded.
As to UUP and DUP, the issues are of course far more complex. For one thing, UUP is far more "British" in outlook.