Sorry for taking so long, had a Dementia moment. From the runs I've done recently it's pretty easy to get to a point where your scoring heavily outclasses the points needed to win the round when you know what you’re doing and what you need, so I've thought of a few different ideas that could help.
1. Tower Change: The 'Tower' Building should probably be changed to maybe 1/7 or 1/8 odds to grant a star, as having a lot of them grants a huge amount of stars, leading to very easy point scoring, especially combined with the next building.
2. Sawmill Change: The 'Sawmill' Building is very op when combined with the 'Tower' and another building, and so you get an insane amount of doubling, sometimes so much that having one tile with like 9 stars could be enough to win say round 15. I reckon the change should instead be 1.5x the points, as 2x is very powerful when done right.
3. Waterwheel Change: The 'Waterwheel' Building, combos heavily with the 'Sawmill' and 'Tower' building, as getting 2 points for having the tile scored is pretty damn good, and from the way I can tell, it doesn’t score it once but multiple times if there are multiple of the same card played. A good change could be to only have it give 1 point, which would lessen it’s ability to be a major way to score points, especially if you have multiple.
4. Bank Change: The ‘Bank’ Building is arguably the best building in the game, as getting money for all the buildings you have makes it far easier to break the game and get all the cards you want. A way to do this would be to change it so it doesn’t count itself as a building at the end of the round, thus decreasing the amount of money gained. You could also have it so each next Bank would give half the money of the first one placed, thus against decreasing the amount of money gained.
5. Discards: Discards are one of the best things to have lots of, as when you have a lot of really good cards, whether it’s a scoring piece or buildings, you want to be able to find them easier. So I have a few ways to change it, you could have the player start with less discards, forcing them to have to manage more with what cards they play. You could also have it so buying more discards is more expensive, you could do it by having it start at maybe 10$, and then having it increase by either a bigger addition or multiplication.
6. Hand Size: The hand size that we have can also be a reason as to why it’s so easy to get a very easy run, since by placing down all your cards you get to grab more from your deck without using a discard. A way to make it harder could be by either increasing or decreasing the hand size, a size of four may give an extra card, but that’s an extra card that’s needed to play if you don’t want to use a discard. Now a size of two would either force them to get creative with their cards or have them use a discard, which limits their ability to find the cards they want.
So those are the ways I thought of to make the game harder and force players to get more creative with how they set things up. Now there are some things that would be great to be added that are more QOL stuff, such as being able to remove a card from your deck, leveling up a tile, giving it a modifier, increasing hand size, choosing where the next castle spawns, all of which would have to cost money to do.