I think Alonzo has captured many of the important factors that go into the WAF/SAF formula. There is one, at least in my home, that seems to only apply if the receipts are discovered: The WAF/SAF is inversely proportional to the cost.
This can of course be partially offset by flowers (minor offset), jewelry (major offset if it includes faceted stones) and the completion of items on 'the list' (variable. ie, did it take longer than the speaker/equipment build?)
Removal of the popcorn ceiling, application of a couple cork walls, total remodel of the vanity area, installation of new flooring/carpet, and fresh paint in our 'master suite' seems have bought very high WAF/SAF of my little project recently detailed in the S3X category (Sex for 1 and sometimes 2). A small price to pay...
Karl