Responding to this as someone who follows the rules and owns at "expensive" resorts (heck, what resort ISN'T expensive these days?), it is more than a little frustrating to see rental ads for obvious Interval/RCI trades into my home resorts. I paid/pay a premium to own there, and supposedly have exclusive rights to rent the weeks I own. When someone gets lucky and is able to trade a low cost/demand unit for a 1, 2, or 3BR Marriott Hawaiian resort (as an example) to use as a rental, it increases supply and weakens the price on the rental market.
Sure, my travel plans have unexpectantly changed sometimes (babies, military deployments, job transfers, etc.), but I've always been able to find a friend who could use my exchange reservations if we couldn't. Just last month, I gave away a week in a 2BR at Grand Chateau in Las Vegas to a Tugger. I figure it all comes around.
I'll add that if all exchange weeks were available for rent, I think it would get harder for the average owner to make good trades than it is now. The sophisticated owners/renters would get very good at picking off prime weeks to use for rentals.