The sand I have now is from the ocean floor, filled with lots of worms, sea stars etc, so I am thinking about keeping some old sand and mixing with new. I like the idea of having a bare bottom tank with SPS (easier to clean, etc), but at the same time, I like the look of coral sand.
As for the tank being full.....sure, there is some room for growth, but right now, I have very limited space for each coral to grow out in all directions, which is my goal. The more room you can provide, the better in my opinion (unless you are in the business of selling coral).
I do have monti caps in my upstairs reef. They grow to fast to add to this reef.
Black starboard is another option .... Sand, bare bottom or starboard......so many options!