If its a 64GB SSD, leave it as a cache - this way you don't have to fool around with fitting in apps and running out of space. WEI isn't that great of an indicator with the cache because the Intel SRT attempts to intelligently cache data you access frequently. WEI is probably not using such data.
If you have a 120GB SSD or larger then you should use the SSD as a boot drive!
hed get a better benefit if he made it his main drive.
i have a 240 gb drive but i am under 60 gb used right now and i have bf3 and 3ds max on it. both huge programs.