Honestly I think releasing gameplay footage is completely pointless, and no, I don't think it would improve sales whatsoever.
Firstly there is the issue of the medium with which people would view the footage. Predominantly it would be YT, which incurs hugely damaging compression artifacts to seriously compromise the visual aspect of the comparison, and it is limited to 30fps, obviously completely missing the performance aspect. So anyone watching this hypothetical footage on YT is going to be under the impression the upgrade is not particularly notable at all. But of course YT isn't the only answer, for the informed and quality concerned around these parts, they know of Gamersyde, downloading directly linked videos ND could host (although their site completely shit itself due to the very first little teaser video).
So who's benefiting from this video? The people who know about Gamersyde, and have a PC which can comfortably display 1080p/60fps video, or they could copy it to a PS3 and play it back. That audience is not only fairly small, they're also informed enough that they know exactly what to expect from a Remaster and if they want it or not.
I see no benefit to releasing a video, and plenty of downsides.