sand substrate is really pain. my larger tank of 800L were applied with fine Silica Sand. Everytime when I do the bottom clean, the sand easiliy got sucked out. also there is always one layyer of sand at bottom when I open the external filter to clean. as you said, gravel and sand do trap a lot of debris and poo. Bare bottom is good and easy to maintain at all time. my filter is not good enough. I am currently looking to buy a FX5 to replace. I am doing daily 1/8 water change to keep water condition ATM.
at the mean time, I am still think of applying substrate to make a nature look. I like greyish colour