Hikki knows how much her American fans want to see her in concert because every other question asked to her by her fans has been when she was gonna tour, so this petition is not only useless but may actually piss her off.
You can just see it whenever she is asked the question in an interview that it's starting to annoy her.

The bottom line is that she would love to tour in America but right now she is not well known enough to sell enough tickets to make it really worth her while to do so.

The only reason the Wondergirls are touring at all is because they are opening for the popular Jonas Brothers.
Utada would never sell out to open for an American group or band, it would be embarrassing and demeaning to her and she would be mocked in Japan.
Hikki is simply too big to open for anybody.