I am not giving Legal Advice but also a Certificate of Mail is also Proof of Mailing.
As for the $16,000 for 5,000 DRI Points ($3.20 per Point) that price is about average. They always start out at $8 to $9 per Point and come down. I think I paid $2.90 per Point for Hawaiian Collection in January 2015. We bought 7,500 DRI Points. We are happy with DRI. But you have to understand the system. A month after we joined we had 2 weeks in France Booked for the following October.
The trade/deposit of your previously owned week is Club Select/Club Combination. I am able to trade 2 weeks of Worldmark (1week a 2 Bedroom and 1 week a 1 bedroom) and get 15,000 DRI Points. This costs me 14,000 Worldmark Points. These traded in weeks are then available for other DRI Members to use for Cash or DRI Points. I have made use of this option on the Big Island of Hawaii.
You can roll over your DRI Points 1 year. If you do it before June 30th you can roll over all your Points. If you miss the June 30th deadline the % of DRI Points you can roll over goes down. I always roll over my Points at the start of the Calender year. You can still use them in the current year but that way they are saved until the next year just in case.
Also DRI has the Internal Point Saver. This is Booking a DRI Resort between only 7 and 60 days before travel. It is normally for about 1/2 The normal Points. So right now I could get a 2 Bedroom for a week at The Point of Poipu in September for 5,000 Points. Or a 2 Bedroom for a week in September at Cabo Azul in San Jose del Cabo with a partial Ocean View for 7,326 Points.
The biggest draw back to buying DRI Points resell is that you can only Book directly into the Home Collection in which the resell Points belong. So if you buy resell Points in the USA Collection you CAN NOT Book through DRI directly into Hawaii, Mexico, Europe, etc. You can trade through RCI etc to go to a DRI Resort in Hawaii or Mexico. Then you have to pay the RCI Fee and at the Resort you are not treated as a DRI Member so you have to pay the daily use fee of $25 or more per day.
So like I said before we enjoy our DRI but you have to learn the System to take advantage of it. It gives us direct Booking into Europe and Asia without having to go through a Trade Organization. Something we did not have with Worldmark. It gives us more options in the USA, Mexico, and Canada.