To take full advantage of SSD Drive, first you must install Windows 8.1. I have a Samsung 840 Pro and it dramatically improve game loading time when zoning, especially loading NPC and when in Moh Donah and Gold Saucer. It also a must have if you are doing Hunt and any Raid Contents.

There is also benefits of having SSD as main Operating System. Boot time for me on Windows 8.1 to the Desktop is 20 seconds. Your system may varies depend on Ram and CPU.

I say it is worth it. Other then that, more Ram also help since if you don't have a lot of Ram, it will slow down once it doesn't have enough Ram to load more textures in the game.