Realistically, i think we have now reached a point where regardless of them being dirty points, there is no resle value. The ability to offload these points to someone else is reward enough in my opinion, in order to relinquish any further liabilities. Depending on what you want out of the club even dirty points are of use especially when you retire and wish to spend 3 months or more abroad in Spain for a fraction of the cost to a non member. I see little benefit in using them for any of the benefits as they are so weighted in the clubs favour, that you would be better off purchasing the same outside the club, so would only really lose out on the variety of resorts you can book.
I feel i am in the minority, but never thought they would have a resale value from the minute i bought in, and cannot see the appointment of an agent changing this, it will just help shift them for you. Timeshare is surely an investment in holidays, secure in the knowledge that the standard of accomodation is guaranteed, and you holiday with people who have similar wishes and values. Anything in addition to this can only be a bonus.