For Windows itself, an SSD is nothing short of vital.
For almost everything else, its placebo.
For example, all of my systems, including my Laptops, have C: as a 120GB SSD, but the Data/Apps are on normal HD.
I tend to prefer WD BLack as they are faster than normal HDs, but my D: Drive on my main PC is 2x2TB WD Blacks and this is used for all my games and apps and E:, as its morlty used for Media, is a basic 2TB Seagate.
In honestly putting MP3s and Movies onto an SSD would not benefit me one bit. Hell, most of my movies and TV progas are on the NAS Drives.
Also, just for the kicks, I have done some messing about with RAM drives, in my main PC, my Gaming PC, and my server, purely for the hell of it, and I have found that the games I play do not benefit in the slightest from being stored in RAM other than actual loading times. I think with Dawn or War 3, the game does automatically save your game as you go along and on the HD, its a 2 seconf wait and when in RAM, its still a 1 second wait, so you have to ask yourself... An SSD might save me one second on a game... MIGHT... Is it worth the money?
Not now it isnt no, but SSDs are coming down in price and its only a matter of time before HDs wil be replaced by SSDs as a viable option, and then, you would be an idiot NOT to go SSD.
But for now... Use one as your C: - thats not even a debate, but for your games etc, its just not worth it that much...
I think if you play only one or two games, then maybe if you only have them installed on an SSD, then it might be worth considering though.