Is there a way to revert a tile to the empty checkerbox tile?

Aside from the overall Reset, it would work like adding/removing Tiles does normally. For example, Left-click to place Concrete, and Right-click to remove Concrete.

I'm playing seablock and it seems I can't remove land or water tiles at all. Not a big deal, just a visual annoyance...

I tried and I see what you mean. I think it's because the lab/sand/landfill/water tiles are considered a "lower layer" that can have other tiles placed on top of them and then later on removed, which means they themselves can't be removed to reveal a lower layer. I don't think I should reorganize the layers, so the best I could do is a "soft reset" that only resets the tiles; that is complicated, though, and I'm not certain it's worth it.

For me, my Sandboxes only last a short while, before being reset to work on something else. A few minutes/hours every now and then. Do you use them more long-form, not frequently resetting them?

Yes, my blueprints tend to be fairly large scale, thank you seablock... I also find myself working on multiple projects at once because I'll get bored of one or something else becomes more pressing. When I'm sure I'm done with something I just alt+D delete it. I haven't done a reset yet.