Hello Profwillis, Bill, welcome to Stamp Community.

Any collection has a value to the collector and that value is what is sometimes missed by people inheriting or acquiring such a collection. The real market value however, is sometimes les and sometimes a lot less.
Some colelctors may have bought stamps as an investment back in the years when stamps were considered an OK investment by the government and you could value thngs at catalogue value.
But to sell to someone who is then only going to sell them over time to someone else and needs to make a profit, nowadays, you will take a loss seemingly.
If you yourself collect then they will be of value because they are from family. But if you are moving them on then show them and sell them.
Any concerns about any high balues please photo or scan and ask here on an appropriate forum area (eg USA in a USA forum).
The blocks of four are still collected but not as much. The special event covers are also down in price and some do still like them. Anything of real nice eye appeal and topical interest or historical interest will be worth something to those interested of course.
Do some searching on
ebay or on here and see what you think and then ask questions all around. If you don't ask, you won't find out.