You didn't mention Massanutten; maybe you've been there, done that
It's a short drive from Northern Virginia and there's so much to do both indoor and outdoor for families. There's probably extra vacations available with RCI and it's probably a very easy exchange. I can't comment really on the Poconos. In 24 years of timesharing, the Poconos was the only negative timesharing experience I've had, so I've never been back. As far as beaches (Virginia, North Carolina), it's off-season and really not much going on or much to see. Williamsburg has things to see of historical value, but naturally Busch Gardens and Water Country aren't available. Plus it will probably be cold when trying to walk around and see Williamsburg. Whereas Massanutten has the indoor waterpark, indoor pools and rec centers, planned activities, as well as snow tubing, snowboarding and skiing.
OOPS, nevermind, I see in another thread that you will be at Massanutten the week after Xmas and that you are an owner there. I'm sure you probably don't want to visit twice in the same month. Oh, well!