Sorry Robert, I have to disagree a little about MTS only burying themselves and going no deeper. I recently pulled a complete mass of Val nana from the back of my tank, where the sub was at least 5 inches deep, and the (very large) root mass had large MTS all throughout. I spent a few minutes picking them all out, I don't see how some of them were any closer than 4 inches to the top of the sub. I've never seen anything like it, it was like they were nesting in there. Granted, the sub they were in was SMS, not sand, perhaps they don't bother digging too deep into the more compacted sand.
As far as sand for planting, I personally have had good luck with regular play sand. The tank in question is only 30gl and I don't think I would do a complete sub of sand in a tank much larger than 30 - 50gl. The depth is no more than 3 inches in the deepest spots, I poke around periodically but not religiously, compaction isn't so bad, perhaps the snails help. I keep a powerhead down low behind some wood scaping to avoid dead spots and keep waste afloat so the filters can catch most of it. Before I added the powerhead, the mess would collect rapidly on top of the sand. Growth was great when I was injecting and fertilizing, now that the tank is low tech (no CO2 or ferts) growth is slow but healthy. Particularly bronze wendtii from Robert, and lutea, it's taking it's normal time but doesn't seem to be slowed by the sand. There is a large sword thriving in it, and anyone familiar with the root mas of a large sword might suspect it's helping against compaction. Ground cover has always been a problem in that tank, which is ironic because I added the sand 3 yrs ago to assist ground cover with it's small grain size. Only E. tenellus would work out there.
My verdict, if I was going to do a biotope type of tank, say with leaf litter or a bare sub as in nature, I would use sand. If I was doing a show tank with ground cover and the whole nine yards, I would only use sand as a contrasting element, one bare area set off from the plant mass.