We have a pretty similar concept! I like the investment mechanic. I implemented several types of dice in mine but I ended up using only two, one normal and one to simulate wounds, I didn't find a way to add the improved dice (I didn't have time to implement more than one fight anyway :D)
It's too bad you can't stack dice, more so when you reach the third fight where the monster starts dealing massive blows. I really liked the characters' design!