Dunno why you would regret it, other than the fact that they aren't really trees, but more internal branches. That said, I think the fact that they regenerate so quickly, and that people seem to be doing a decent job of watering and petting means that dusting the magic forest is redundant and not really worth the effort. So, maybe that's the regret: that you wasted dust where it wasn't really needed.,,
1, dust wont work, and trying does not use it up.
2, growing the tree full will net you more planks BUT
3, each tree can only be petted, watered and harvested once per glitch.
4, so it does pay to clear because each new seedling counts as a new tree, even if you only grow it to one section of tree then clear it 10 to 25 planks, you will have another new tree in a few minutes.
5, they don't die so don't count to clearing achievements
6, they do count to wood petting/watering achievements
7, the trees will grow without pets and waters but its worth the effort
hope all that helps :)
Only problem I can foresee is if when wood is in high demand it all turns into another version of Ajaya Bliss with some people instructing others to dust and harvest efficiently (maybe in groups) to get maximum yield.
Actually, I think it's considerate to reduce them to seedling. See jiva's post above. When they are cleared and grow back they are a "new" tree and can then be harvested again. So, more harvests, more wood per person. See?