Should work fine I say.
I meant to post back just after Christmas but have been too busy playing with my wii.
So as you guessed my Spanish Wii works perfectly in the UK (all it needed was a plug adapter.....99p off ebay).
It has all English Language on it, and plays both the Spanish Wii Sports game in English fine, and also plays all the UK games I've brought for it fine in English too. Wifi is fine and so is downloading games, and the weather channel is correct too.
Only the instruction booklet was not in English, but its not rocket science to work out what to do.
So get importing guys!!!!