TL;DR: "Cheat" in some Sand
I spent the last few days rethinking my reasons to need a sand generator, which were:
- A need for really large amounts of Sand for TNT and Glass
- A wish to keep the natural terrain
At some moment I had a thought in my head: "Why don't I just use a command to give myself a needed amount of Sand?".
In original vanilla Minecraft, the problem with acquiring large amounts of Sand is not that it takes time, like with Diamonds (if not concerned about destroying terrain and armed with a Diamond Shovel, one can dig large stacks of Sand very quickly), and not the difficulty, like with the Nether Star. It's about terrain preservation.
So, my solution was to use something to give players large amounts of Sand for nothing:
- Giving Sand away via commands on demand
- Setting up a Command Block
- For a role-playing server, setting up a Custom NPC that gives large amounts of Sand for a token amount of currency.
While it might be cool to find a glitch that could solve the problem and build a fancy redstone scheme, I don't see any real problems rising from Sand, an already common resource, becoming more easily available. Actually, pretty much the same could go for other common and easy to obtain resources like wood (as not all the players replant their chopped down trees).