I think it's a wise decision. Like it's already been said, you can always add a shallow or even deep sand bed after the fact. Alot of the bb tanks that are established you don't even notice the bare bottom till you really look

Here is a couple pics of my tank from a while back. You can see how corals will spread and cover the bottom if you give them time. And the coraline doesn't look all that bad.

http://i406.photobucket.com/albums/p...0/IMG_1909.jpg

http://i406.photobucket.com/albums/p...0/IMG_1912.jpg

WOW. Nice tank! I wouldn't even have noticed the BB....go figure....