I think that as we get more sites, this problem is going to become worse. We already have a few potential areas of confusion, where sites have defined areas of expertise that are close but not the same. Creating a separate dispatch site may not be necessary, though. We already have a site that has experts in the Stack Exchange network, or at least expertise in creating sites. Medium- and high-rep users on Area 51 are quite likely to know the network well and could help migrate questions.
A dispatching function could be part of a Q&A board on Area 51: New users could simply ask their question there, and I suspect that there would be users that would not only facilitate migrating the question to the correct place, but advise them on SE etiquette.
I've seen a few remarks here and there that Area 51 rep is kinda worthless (I disagree), and this would address that. A bonus to this might be to filter out some of the newbie forum-style posts, and keep them away from the boards. Tying area 51 rep to how much you help new users get started would be a great incentive.
In short, using Area 51 to stage new sites and new questions from new users seems like a logical next step.