Is there any benefit to cleaning the piston crowns? Seems like mine might be in the the high-risk, low-reward box. ¯\_(ツ)_/¯

 

Not really. They will start to dirty back up after a few thousand miles.

 

Depends on how much buildup there is. I always clean off any carbon cake because it can lead to hotspots and pre-detonation. It does look like you have some accumulation in several cylinders.
Change the valve stem seals, of course.