I've also asked for a pixel snapping tool before, but nobody really considered it very useful since when you have a lot of rotations the children bones will never be at pixel perfect positions. I've still haven't found a workaround for this (now working on pixelated games with spine features just like you), but keep in mind that having a pixel snap tool has one more complication:
Spine takes the center of an attachment for the reference point of that attachment in order to state its position. When you have an attachment with odd number of pixels in its size, the center of that attachment is "half a pixel", so if you want to pixel snap that one you always would have to manually move that attachment half a pixel somewhere.
So the pixel snapping tool would have to work differently when positioning bones, or positioning attachments. Probably the quickest way of creating this tool would be to have a hot key to pixel snap bone-translation positions, and we would still manually position attachments as we do now.
I still think it can be a very useful tool since when you are mixing pixelated raster animations with spine the tool you use the most is the translation, not the rotation, and personally I use a lot of stepped curves for having that retro-vibe.
I think Spine is a very useful tool for this kind of things and It allows you to do complex big bosses and stuff as It happened in gunstar heroes, sparkster and those kind of games. I completely support your idea and wether they add it or not I'll probably write a post with the workflow I use for this kind of thing when I have more material of the game I'm working on.
