I'm very opinionated on this one. DON'T TOUCH IT!!!! If your tank looks good leave it alone. And since when do the bubbles mean the DSB is working??? Think about it, the bacteria and microfauna will have their habitat cut in half if you take out half your sand. You can never have to much sand.
But, if you do decide to take it out, please call me I would love to come get it from you!
Adam