If you really do want to make a statement with your dollars, then import and support the company (NoE) that actually took the risk to localize, advertise, and support these games coming to an English-speaking market.
But you might be making the wrong statement. I don't know if NOE can distinguish between import and domestic sales, but if they can't then you're just transferring sales numbers over there. All that would do is help justify that NOE releasing the games and NOA not putting them out was a good idea. Buying multiple NA copies would be better since that pushes NOA closer to breaking even on the whole deal, possibly convincing them to bring over the other two rainfall games.
The problem is that messages from "statement buys" are always fuzzy.
If Xenoblade doesn't sell well in North America, there is no single reason why. Is there no market for JRPGs that are critical darlings in this region? Or is releasing games - especially new IPs - without adequate marketing and support a bad idea? Would poor sales mean that whatever core audience the Wii once had has moved on after the painfully barren year that was 2011? Or that limiting a release to GameStop and online preorders directly from Nintendo isn't a good idea? Maybe being the last region to release the game (by 7 or 8 months) and repeatedly stating that there are no plans for release in this region actually affects buyer interest?
I still think that:
(a) the company that actually made a
real effort and took the financial risk to translate and release this game in English (without grassroots efforts showing support, and GameStop subsidizing the production costs)
deserves to be rewarded. Remember that if we do see any of the other rainfall trilogy games, it will be directly attributable to NoE's commitment to making them available and not any action from NoA.
(b) there is no reasonable way that NoA will be interested in releasing the other rainfall games after a new Nintendo console has hit the market. Given an eight month delay between when Xenoblade was released in North America, and assuming that Wii U really is launching in 2012, that makes me very skeptical that The Last Story or Pandora's Tower will be released here.
(c)
people should buy Xenoblade because they want to enjoy the game, and not for any other reason. Having played the game, I can assure you that it's worth owning for any RPG fan.