That's a remarkably thorough writeup for a game where you buy motivational posters for monkeys. (No one ever talks about the infinite zookeepers!)
I can think of things you could add to the game. For instance, I went away to take out the garbage, and when I came back, I had missed several words! So perhaps a button where you can review the script as they have it so far. Or: I wonder what would happen if, each time a monkey gets a letter right, they have a slightly better chance of getting that letter the next time it comes around--not an overall improvement, just a stimulus/reward so that now they know what's expected when they see an "A".
But those would be additions. I can't think of any way to improve this game, because it's a game about monkeys typing Shakespeare letter by letter, which makes it perfect as it is.