Alef:
I have always feelt Coover's novel to be strangely unerotic
I'm with you on this, Alef, and the reason is that it was never designed to be erotic. I understand that it was written to make the point that pornography is seldom erotic. He strips the story down to it's basic elements and then runs it on a loop with only the smallest of changes between each scene, a change of implement perhaps or a different fetishistic item found in the bed.
There is little plot, no characterisation and no sense of place (other than perhaps a mental stage set) and only the spankings have any description. In short it lacks any sense of fleshing out which, I think, is essential for eroticism. This is entirely deliberate from Coover and it is very accomplished writing but it just isn't sexy.
In other Coover works, spankings are mentioned in asides, (Gerald's Party, Pinnochio in Venice) and these have more eroticism than the whole of Spanking the Maid.