I think if you did WordCamp North for US/CAN and a WordCamp South for those in central and south America you'd be continuing the continental precedent set with WC Europe. Matt said that WC Europe has been a huge success and most likely is fostering continued growth of local WordCamps so I do think there's room for both. I love the idea of investing in a smaller market city too. With a WC North you could also alternate between Canada and the US.