I disabled the auto-update and now the disk icon doesn't stay on for hours anymore, but the interface hasn't sped up at all.
I noticed that if I start a song, wait for it to start, leave it for two minutes or so and then operate the player, the interface works correctly for a while, with instant pausing/unpausing. I can even change a few songs, but then the slowness comes back.
It did this even with its old microdrive, but I scanned it and discovered it was full of bad sectors, so I presumed that was the reason. Apparently it wasn't, though.
This can't possibly be normal. Do your rockboxed Minis work like this? (I'm pretty sure not, but it never hurts to ask.)
NSX: I'm pretty sure Sandisk cards aren't full-ATA.