At first, I thought they were color guides, too, but some of the handwritten notes threw me. They probably are color guides, but I am not positive.
Color guides have varying worth, from a little to maybe $2-400. Usually, they are in the $25-75 range. As with most things, it depends on the colorist. I have 2, one by Neil Adams, for which I paid about $350. The colors he chose, by the way, are not, in some cases, the ones on the published cover. I liked his choices a bit better.
I certainly agree with you that those acetate reprints should not be considered original art. They are purely decorative.