I like J10's idea, I think it would be great to port over main builds onto a newly regenerated copy of the same seed if possible! My town is isolated to just an island!
So I don't think this is a bad idea, however I would be concerned about the land regeneration at my base due to me having to do huge terraforms in the area to get the look I have now (tons of gravel). Would towny transfer over as well?
If it were up to me, I'd be lazy and copy-paste entire chunks over. Not just the ones covered by towny, but also to a two or three chunk distance from the borders.