I find that after a short bit, money is easy and very rarely a problem for me so wouldn't it be cool if you could make the game harder by random events like server malfunction or employees demanding more money or even rival MMORPGs taking away subscribers . These features should all be optional but it adds a bit of challenge to this otherwise easy game.
You could also make it so you gain less subscribers and more bugs and even more cheaters.
But with all this said not everyone would want it to be harder so make these features all optional for those who want them and those that don't.
Thank you