I don't think the issue is necessarily overvaluing them, especially if there is legitimate sentimental value (ie. First gun, fathers gun etc). My first rifle was a New Haven M70 featherweight, it was stolen a few years ago and I would give up any of my several thousand dollar rigs I shoot now to have it back.
I think the bigger issue that we as enthusiasts can be blind to is that our hobby can easily become an obsession to the point that it is our religion/second mistress etc to the point that what we see as a huge value is actually a bad memory for those we love. My father was very prescriptive in the way he taught me everything growing up, either by beating over my head how NOT to do something or by describing exactly how it must be done, no exceptions. It got to the point where as soon as I finished hunter safety and was old enough we stopped hunting together entirely because we would fight the whole time. We've since grown closer (getting married and having kids of my own helped) but at the time I wanted nothing to do with his hobbies.
It's sad when we see someone we look up to die and their family doesn't seem to appreciate what they had poured their soul inot, but it should be a cautionary tale for any of us to make sure we are teaching our own children to love and appreciate what we do and be very careful that in pursuit of what we love we aren't alienating those around us. Those families sold all those guns because for however much those men loved them, it certainly appears to have not been shared by those closest to them. That's the really sad part.
When I die, I want my kids to fight over the nicer guns in my collection, not because they appreciate the guns for their value/quality, but because of the memories they shared with me via those tools.