Whether a fast SSD will help you or not really depends on what sort of work you're doing, and what resources are constraining you now.
Look your CPU usage while rendering. If your processors are working at or near 100%, then adding faster disks won't help.
That said, I believe Adobe recommends three drives: one for the application and operating system, one for source footage, and one for render output.
Walter Soyka, Principal
Keen Live, Inc.
Presentation, Motion Graphics & Widescreen Design
RenderBreak: A Blog on Innovation in Production
