On the first point-- what you say is clearly right, but is also consistent with the notion that there are certain mathematical commonalities which hold across the various 'flavors' of pleasure, and different mathematical commonalities in pain states.

Squashing the richness of human emotion into a continuum of positive and negative valence sounds like a horribly lossy transform, but I'm okay with that in this context. I expect that experiences at the 'pleasure' end of the continuum will have important commonalities 'under the hood' with others at that same end. And those commonalities will vanish, and very possibly invert, when we look at the 'agony' end.

On the second point, the evidence points to physical and emotional pain sharing many of the same circuits, and indeed, drugs which reduce physical pain also reduce emotional pain. On the other hand, as you might expect, there are some differences in the precise circuitry each type of pain activates. But by and large, the differences are subtle.