Alan keyes has standing.
Because they're all Democrats who could ill afford to alienate the black vote by disqualifying O. If Hillary had moved early on, over a year ago, before the primaries, when O was struggling to prove his creds in the black community due to his elitist background, she might have had a chance. But with whom would she have filed a challenge? It was certainly too early to consider him a viable candidate, since she was then considered a sure bet to be the nominee. It would have looked extremely mean-spirited to attempt to DQ someone who was a) touted as the Democratic hope of the future, post-2008; and b) not favored to win over Hillary. Later on, when he became a contender, it was too late, since she would surely have generated outraged charges of racism.
The same goes for John "Jermiah-Wright-is-Off-Limits" McCain, in addition to the fact that the NY Times, various liberal lawyers and Congess itself had raised the issue of his own eligibility well before the Convention.
As far as standing goes, Donofrio's charge was that all three candidates (including Cordero of the Socialist Party) are not "natural born," and were therefore ineligible to appear on the NJ ballot. He claimed that he had been harmed as a NJ voter in not having a choice of a Consitutionally qualified candidate to vote for, and that the NJ SOS was derelict in her duty to investigate the qualifications of the candidates (Cordero's not even a citizen). He filed before the election, asking that the vote be halted until the issue was addressed.
In denying the suit, the NJ SC used the argument that the SOS's duty is strictly "clerical," and it wasn't her responsibility to to verify the credentials of the candidates. They didn't mention the question of his standing in their opinion.
I think the chances of SCOTUS taking up this case are exceedingly slim, but not for the reasons presented above.