Pretty fun little game. Short play time but is indeed relaxing.
I can see that balancing isn't the key here. When a player makes an investment they guarantee a set amount of return, given enough dice rolls.
If you want this game to be more strategic, consider letting the buildings decay when their number is not rolled. (either every miss, or appoint a specific number that will trigger their decay.
With a decay trigger, you may also want to increase their hp to balance it out.
I mean, it's still your choice, coz it's totally fine to not punish the player at all.
After all, we don't just play to be challenged at all times.