Why mplayer only? Many video types could be played with hardware acceleration, giving performance boost, through mafw. I would keep mplayer (CPU decoding, only) for things that won't work with mafw.

Considering, that your decoding performance (using mplayer) depends solely on CPU power, I would consider overclocking upper limit to insane things like 1150 mhz - as you said, device is quite dead already, so risk of problems in 3+ years isn't important, "methinks". Just don't *lock* it at 1150 mhz - limits like 500mhz-1150mhz should give quick enough reaction time, with super-power allocated, when required.

Also, remember, that you need to disable smartreflex, as it works only up to 900 mhz (in case of kernel-power, otherwise it's broken, totally), but it shouldn't matter, as your device is going to be powered from charger 100% of time.

As for stripping unnecessary components, without losing basic functionality, you should attract attention of user reinob - AFAIK, he went further than anyone else, in stripping components.

/Estel