Meh i've finished thousand needles low 20's (by finished i mean all quests i can get) The more chars you have the quicker you get through the quests, and the less xp you make along the way
Was the don't say ashenvale put me off, cause if he's too high level for thousand needles then ashenvale would be a waste of time...
Thousand needles is 20-34, so I'm guessing if he has truely finished there (ie all quests and is not stuck) then it is a complete waste of time going back to a level 20-30 area.
If however he's hit a spot where he's stuck (ie too low level for most quests, like happens to me all the time) then depending on his level where he goes to make up the lost xp.
Assuming you've finished completely, which would place you early 30s, then your options are Alterac, Arathi, Desolace or Stranglethorn