]Theoretically one can do a trade to get into a DVC property, but I heard it's pretty near impossible at Grand Californian. [/B] When a timeshare was being pitched to us, the salesman was showing us the number of points needed. However, I know this is highly contingent on space being available, and frankly a regular timeshare owner will probably be last in line for any opportunity that comes up.
DVC is interesting in that Disney holds the right of first refusal on sales. They rarely go on sale on the open market because Disney will typically buy it back. So they maintain their value really well. However, the costs are also pretty high. There are other timeshares that people are literally trying to dump for free just so they can stop paying the maintenance fees, but DVC isn't like that.