I would suggest crosspath on buildings like from the Tower Defense genre so instead of spamming building, there would be more variations like more people per building and some cool abilities. This should be able to give performance boost instead of having a bunch of woodcutter cutting down a million trees.
You could try to introduce new threats like enemies since the flood is not much of a threat since the game progression feels so linear, but defeating them should give a reward which incentivizes the player to defeat them. This is just very optional suggestion.
For difficulty, you could try to have 3 but it's up to you where there is peaceful (just no enemies and a relaxed gameplay), normal (enemies are present and flood rises a little bit fast), hard (enemies are much harder and flood rises fast). The "weights" system also make it have a feeling from those roguelike games so you could try to expand them, and don't feel afraid of going extreme for it.
It's up to you to expand the game especially if you still focus on the woodcutting theme, it's only how it is much more like a one-win game so improve on that part and good luck!