It'd definitely be worth it if your game was commercial. And if you spent enough time on it. $500 initial, If you sell it at like $5 a copy, that's only 100 copies.
That's actually not a bad deal. If I was going to make a commercial game, that's what I'd do. But I don't have enough interest. Or time. Although money isn't too bad. $500 just means I work a little extra one summer, or spend less money on stuff that I don't need and save more. If you can't come up with $500 for something you really want, you probably either A) don't have a job, in which case you are either not old enough or already rich B) can't save money or C) don't really want that something. Or D) live in some poor country where the annual per capita income is around $7000. In which case, how do you have a computer with internet anyways?
Anyways, I'd wait until you get an actual start done on rmxp before buying anything. Make sure that you can actually do this. Because judging by your personality, I'm gonna say you can't. Commercial games require a coordinated effort from a huge team of people. Ever seen the credits on a video game? yeah... So stick with rmxp until you are sure you can take it to the next step and succeed.