There may be a little bit of extra value as compared to `94-`04 rifles, since the prebans will likely be in AW config, but the 94-04 rifles will need a new upper/telestock.
There should be a small delay between the sunset and the demise of the 94-04 rifles, as dealers, distributors, and manufacturers clear out inventory. During that time I expect that pre-94 rifles with matching uppers will have a little higher value than 94-04 rifles, since the owner would need to refit the features or swap out uppers. Similiar to how shorty Prebans command higher prices than a 20" preban plus the cost of a new upper.
So, for a while, I'd expect the prebans to be worth more than postbans, but only by the cost of a new preban upper minus the sale value of the old postban upper.