Since we are such WDW Freaks we haven't done this very often but when we've looked at using them outside of Disney for skiing trips to vermont or during our college road trip to California, Arizona & Vegas we found that due to the amount of points per night it made more sense for us to rent out a few of our points and just pay cash for a resort. We alway give our points a $10.00 value/point and most of the places we wished to stay at took 25 to 40points per night so that would be 250.00 to 400.00 per night - we could get the room cheaper by just booking and paying cash and by renting our points we were able to pay for our rooms and then some. And not use all our points so we could still spend at least a weekend at our favorite place.
My advise is do your homework, give your points a $$$ value then multiply that by the number of points needed per night at a non-disney hotel.