We kind of had a similar dilemma when we were getting ready to book our cruise. We had points but by borrowing and banking we were just short some points for our 3rd person. So dh sat down and figured what the cost would be to purchase X amount of points and what the cost was to pay cash for the person. We talked and my suggestion to him was logical - why pay X amount of money for the 3rd person for a one time shot when we can pay that plus a bit more for X amount of points that we can use for the next X amount of years.
Now that worked for us because we don't go every year. So you also have to look at that. If you go every year, are you going to have points left over to use the following year for a trip or will be upset because you used your points for the cruise and thus won't have the points and have to pay for a room. That would be a similar thing if you rented out your points. If you rent out points and don't have enough for another trip - is that going to disappoint you later or will you put aside some of that money to pay for your room?????
If it were me, I'd use the points. But I can sure see Robin's side of it as to the comparison. You also run the risk of not being able to rent out enough points to pay for your cruise, then what happens???