Regarding the rubble, the pieces will not show up faster by putting the rubble back - the pieces ONLY show up after the rubble is removed. Additionally, unlike other collectibles, tablet pieces only ever show up once - you will never get a duplicate. Depending on how the game selects the next collectible to appear, this may mean that the tablet pieces become less common as you collect more of them.

I can't post my method here, partly because it breaches forum rules to post it here, and partly because it doesn't actually work. For instance, the grove is listed as unsolved, but the trees don't go away. So . . . yeah. It's broken. Forgive my bragging about such broken methods.