I don't know whether the Before Watchmen books will be worth reading, but I know they won't be worth publishing for at least four reasons:
1. Before Watchmen already exists. It's every superhero comic ever published before Alan Moore and Dave Gibbons created Watchmen. The point of Watchmen is it's the culmination of the superhero comics everyone knew.
2. Before Watchmen is a prequel. People don't want to see a backstory fleshed out that only elaborates on what they know. I haven't read Before Watchmen and don't plan to, but I suspect DC has created their Phantom Menace.
3. DC's reason for doing Before Watchmen isn't artistic. It's pure Capitalism 101: when you have something that's profitable, milk it and shear it until it's time to send it to the knacker.
4. Before Watchmen is designed to be compared to something that's greatly admired. Working on Before Watchmen would be like working on Before Casablanca: Do you really want to be despised?
As for DC's decision to make Alan Scott—the Green Lantern they don't promote much, the Green Lantern on the "alternate" Earth that's not the one that counts in the DC universe—their gay superhero, yawn. They're right that at least one of the original 1940s superheros should come out of the closet, but if they want to make a meaningful change in the DCU, they also need to out a hero who was relevant in the '60s, a hero from Earth One, the world that matters to casual readers. I suggest Elongated Man or the Martian Manhunter, even though both of their names inspire obvious jokes. Or better yet, Hawkman—a gay Hawkman and a straight Hawkwoman could make an entertaining duo.