Let me give you guys my opinion on this One Piece: Unlimited Cruise subject.
At the time of the game's release, One Piece was doing extremely well in Germany, and people noticed that there were no other ways to get One Piece aside from the anime. UC was the deal breaker, because the series sold well in Europe (possibly 2nd from Japan), more money was indefinite and thus, UC was released.
The reason I believe that UA wasn't released in Europe was because NamcoBandai already were working on UC when UA shipped to the US, and possibly felt that since the Europeans don't get UA, they'll make more money be sending UC to Europe because Europe didn't experience the game mechanics of UA, because lets face it, they're both practically the same game in terms of design.
With the announcement of OP:Gigant battle this summer in Europe and a possible release of UCSP, it was proven that the Unlimited franchise was a way for the company to see if One Piece was popular enough to warrant more products in a specific country. In Japan that isn't a problem, since Japan practically eats it up. The US and Europe are different however, which is why this franchise was the perfect test.
So in conclusion, I would say import UC for all you US fans out there, but I think that the Wii freeloader doesn't work anymore. Or, even better, wait 'till Gigant Battle comes to Europe and import that, since DS games have no region lock.