Yup you got it right. Idle Time is what is needed. Depending on which version you have its either an older JMicron controller or a newer one (well actually a Toshiba branded and built one based on a JM design....but very little dif). So you will either need a LOT of idle time or a only a little bit to get it out of its degraded state (ignore the read speed numbers its only write that really tanks when the drives get dirty). IF you are impatient and want to get it back to normal NOW use FreeSpaceCleaner.exe
w/ FF option (aka AS-Clean) and it will write 1's to all the free cells. Then it deletes the file it creates. This will bring all the empty cells back to a virgin state. It will take awhile. Let it keep going unitl it is FINISHED (ie ignore the green bar...it goes up and down and has no real bearing on whats going on). IF you want to take an extra step, do a "TONY-TRIM" which adds a free space consolidation to the equation before running FreeSpaceCleaner / AS-Clean.
Here is a link to OCZ's guide. It has links for AS-Clean.
Guide A simple guide for gen1 owners( Apex, solid, core V1/V2) or raid array owners who want to consolidate free space and clean the remaining Nand on the drives. OCZ gen2 drives..Vertex, Agility, Solid2, TURBO owners with FW 1.5 you do not need this.
DO this ONCE and then afterwords let the system idle every day for awhile to keep it from happening again. ;)
YMMV but thats what I would do.