It is kind of surprising how much more Fri. and Sat. cost in terms of points. We are staying the full week though, because I'm too lazy to do a split stay. It's tempting to move to the Poly for the weekend because I've always wanted to stay there, but my parents are coming with us, and I don't think my dad would be too wild about changing resorts. That, combined with the prospect of having to move all the kids' stuff, was sufficient to convince me to stay put. But we're getting a 2 br villa at OKW for about the same price as 2 rooms at a moderate, which sounds like a good deal to me.
You could always see if there is availability thru CRO for the weekend. I believe it would cost less thru Disney and then rent your points during the week nights.