To Rog's point, if I were to sell my collection now I might consider not breaking out the better items or sets. Basically everything I have is complete set definitives and the collection might be worth more in country lots.
Likewise as I seek to add stamps to my colletion, I do not see price pressure upward on most individual sets or better single items. I started putting together some Mexico recently (definitives from 1934 until 1975 when the Exportas started). After putting several better items on my watch list on
ebay, I started getting a string of unsolicited discount offers.
So this new phenomenon we are seeing with large collections may be limited to multi-volume estates or large country/region lots, and not better sets/singles.