While Mt Snow hosted some epic NORBA DH races back in the day, I've read none of those tracks are currently open for riding and only a few fairly tame trails currently exist.
Windham isn't bad, but there are only a few trails to ride. Two "natural" DH trails - The World Cup UCI course and the Citizens DH course as well as a pair of Gravity Logic built jump trails. I wouldn't go there for a full weekend that didn't involve a race, but it's worth a day of riding. My thought has been to hit Plattekill on Sat and then when done, drive to Windham and get a room there (better hotel and eating options), ride Windham on Sun and then head home.
Plattekill is fun if you know the trails. If you don't know the trails, it can kinda suck. Trail marking is sporadic at best. Some of the trails are so over-grown you have to know where they are to ride them.