If your mac had USB3 (I Believe the one in your profile does)...
USB3 is a
bit slower than tunderbolt, but there are more options out there, and possibly cheeper.
USB3 is plenty fast for most home uses. Even USB2 can handle 3 or 4 raw Blu-ray streams at the same time.
If you're consistently moving very large files (read editing HD video all the time), then thunderbolt might be worth it, but to store a movie and music collection or to use for backups*, USB3 is fine.
to truly take advantage of the speeds of thunderbolt you'll need to load your RAID with SSDs
*just a reminder, RAID is not backup. always have a second copy of your important data somewhere else.