I'm in the minority that didn't really have a problem with Vaan (except for his poor sense of style). I thought starting off someplace local gave the player a starting point to start to care about the broader world, and he could be safely ignored after that. Maybe he could have been injected into the central plot more, but that would have likely ended up corny as hell ("Ashe's long lost bastard half-brother!") -- which would have been especially out of place in the more mature plot development that made FFXII stand out from most other entries in the series.

Plus, he was not nearly as annoying as Tidus or Squall.