You can book 3-6 night stays at some of the Interval destinations (to see them, you have to log into MS website to be able to use their internal link which takes you to an Interval search engine). Go to the World Passport Collection from the Member Getaways menu - you'll find Book a Short Stay now.
As for what points they cost, I can't seem to get any information online from the MS website. You are supposed to be able to book the short stays online from the MS website, so I assume that if you were to select a destination from that search engine you'd eventually find the points for them.