Bill, what you say is of course true in economic terms - value is determined by the parties, but I do not trust someone not providing full disclosure of material facts, and this pricing question I raise is material to me. Disclosethe facts and let me decide whether it is worth the premium of an increase in current MSRP - that's fair.
I would feel dishonest buying something for $2000 when the list is $3,500 and 3 years later trying to sell it for $2,900 when the price rose to $4,800 without disclosing that fact - I just would not do it. I suppose it is a matter of what feels like the right thing to do and I suppose we all follow different rules.
I would not buy a 3 year-old piece of Manley gear that did not reflect the new/used price at the time the seller bought it - but I would buy a 40-50 year old Mac/Marantz selling for mulitples of the retail at the time it was made, and you will find no seller feels the need to hide that fact - there is value in high quality vintage having nothing to do with MSRP.