Odd... I guess the trackpad input sleep removal business applies to your mouse too for some reason, yet not to wireless mice.
Again, dunno what to suggest other than going for a wireless version of the same mouse. I looked like crazy but there doesn't seem to be any way to toggle the Mac OS powering or not powering the laser/LED on wired mice during sleep, at least that Google can find.
I feel like there's gotta be some toggle somewhere though, if for no other reason than I can't keep a wired mouse's tracker powered after activating sleep on any of my machines, even going back to Tiger, yet you were doing it successfully as of Snow Leopard.
Currently playing with Tiger on the G5 while also installing Snow Leopard on my WD Passport so I can boot the MBP into Snow Leopard and see what happens. If I can successfully cause something to wake up by moving a wired mouse, maybe I can get some headway into figuring this out.
EDIT: Yeah, okay, I'm stumped now. Dug into the equipment drawer and located the original black translucent Apple Pro Mouse that came with my G4 Digital Audio and the white Mighty Mouse, same story. Put Snow Leopard 10.6.8 on my MacBook Pro, still can't get power to any wired mouse's tracker while asleep.
At the point where I want to buy a G5 mouse now to experiment with it. Going to put up a saved search on eBay and try and snag one.
Out of curiosity, which model do you have, tBC? The original (silver and black with orange spraypaint in the center) or the revised model (blue-black scaley)?