Does anyone know what the innards of the empeg's rotary encoder are like? Is it possible that it would benefit from a similar procedure

I haven't looked, but I'd have to wonder whether it's worth it. Every time you de-/re- solder the encoder you are risking potential damage to the display board. I'd hate to go through the motions only to discover that my cleaning wasn't good enough and that I had to replace it anyway. For $10 it's probably worth just replacing it to start with. If it were a $40 part then it'd be a different matter. If it is possible to easily dismantle the encoder without desoldering it first (doubtful), then perhaps it's worth a shot.