I've never liked the treadmill approach to retaining players. It just creates a long list of potentially boring things that you need to do before you can get an item that you might find interesting. I agree that the gameplay can be overly simple and this is where I would try to change things. I know that some people want more things to get, but I find that this just makes the experience hollow. I want to do things that are interesting, rather than slog through something generic for a pretty trivial reward and I would prefer if the devs put more effort into making the game fun to play in place of trying to motivate us to do things that we otherwise wouldn't care about.