Aye, Activision is selling the collection for 20 bucks on Steam, they probably want to sell it for the same price on GOG. Otherwise I'm sure GOG would have sold it at a more reasonable price.
If GOG offers more Sierra adventure games in the future, using the same 1-2-3-4 & 5-6-7 bundles deal, I think the solution would be to charge 8$ for the older games bundle and 12$ for the newer. That way you get the same 20$ price but it's spread fairer across the games, even if ideally they should sell all games in a series in a single bundle.
I too hope the remake of the first game will be quickly added to the bundle to compensate for the currently high price.
I wonder if GOG users would complain if GOG removed both bundles from their service, sold all 6 games in a new, single bundle and issued 10$ gift certificate to anyone who purchased the older bundles so they could either buy the new pack or buy a new game.
I'm not even sure they'd need to remove the old packs. I think that would be too confusing, and it would disadvantage people who don't back up their installers. Unselling a game would, I think, be absolutely contrary to GOG's anti-DRM position. (No, technically, it's not DRM, but the spirit is the same.)
But, either way, I do honestly feel like if they just added the VGA SQ1 remake to this package, along with a few extras (at least the soundtracks, which are easily obtained for old Sierra games) the $9.99 price point wouldn't feel so high. But as it stands, this set is just so bare-bones, it doesn't really warrant that price.