I do the same thing in regards to clearing cache... Some programs just demolish it, and as this phone uses Flash Memory (NAND?), the more free space available the faster it operates. It is just like Solid State Drives on a PC: I have to keep my RAID0 Vertex3's below 75% total capacity or performance drops exponentially (I keep them filled to about ~225GB, 2x240GB Drives in RAID0 = 480GB, but when I loaded them up to around 425GB my Read/Write speeds went from ~885Mbps/~870Mbps to 315/270... immediately transferring 125GB back to RAID10 HDD array resulted in identical performance to before).
I do not know how big the total system cache is for Android OS, or how it works compared to Windows (not a Linux guy myself), but as fast as NAND-based Flash memory is, and it IS FAST, it still doesn't come close to the speed of dual-channel LPDDR2 RAM.
It makes sense to keep unnecessary stuff out of the RAM so it can be used immediately if necessary in the case of an X86-64 OS (i.e. Win7) but things may be different here... I just don't know in what way.