I usually use an opportunity cost on my purchase price of 6-7% [blended bond/stock investment return or normal rental property cap rate) plus the annual MF /point. For example, my King's Land property has 14,400 points/year for $1845 MF/yr, or $0.128/point. I also spent $10k to purchase it, which I am currently assuming I will re-coup all or most if I ever sell it. Opportunity cost of that $10k is $650/year (10k * 6.5%) or $0.045 per point per year, or a total true cost of $0.173 per point per year. So a stay that cost 5,000 points for 7 nights somewhere I would say it cost me $865 or so (add $59 if you are charged the club res fee) or $123/night.
[When using my points, I also compare to other options there or elsewhere (cash, hilton honor points, marriott points, free night certificates) for a relative value comparison]