I currently have about an inch of Fiji pink. It's slowly being removed with water changes and I'll eventually be bare bottom.
I do think it looks a bit better than bare bottom to begin with, but don't see a huge benefit as far as biological filtration goes. If got plently of live rock that suffices for my filtration as well as a block of marine pure in my sump. Once the sand gets a bit older, IMO, is not as nice as day one and not worth the hastle of keeping it clean.
I'd rather use that real estate for more coral or frags. Plus, in the time it took for my sand to go from a 10 aesthetically to a 7 where it's now, I could of had the bottom covered in coralline.