Well folks, I didn't expect this one to get as much attention as it did.
I'm now thinking reorganising the columns is going to e bad idea (as far as the table goes).
@jeff - This is a FACT table so all columns are completed (no NULLs) but that's a useful titbit I didn't know about (for the used/unused columns) and I'll keep in mind for future reference. The views sound like a far better plan than my original (now hare-brained) idea.
@Frederico - I've never come across that before, so possibly something to add to the arsenal as well.