I don't think you should think of it as "mastering" the sim. It isn't really a game to be beaten, it's a learning tool. I've been flying RealFlight Since version 2 and I don't think I've mastered it yet. I still crash when I do something wrong. I do like to try new things on it that I'd like to learn for real. It saves a ton of money right there. The most basic lesson is to do new things up high. Nobody's ever ruined a plane by driving it into air.
I'm flying a new CAP 231EX this year and the sim has already saved that airplane by teaching me that it likes to snaproll with too much elevator input. Learning that on the real thing could have been very costly. It did it on the sim, so after I got the real one trimmed out on the maiden flight, I took it up stairs to see if it would do the same thing. YUP!