Why are older tubes so much sought after

We seek out old tubes because the Gilbert Erector Sets, Tinkertoys, Lionel Trains, and GI Joes so popular in our youth are more expensive and difficult to find in mint condition.

And they're cheaper to ship.

if you speak to many manufacturers of tube amps, tube cd players and tube preamps, in production today, you will be told that replacing the tube with nos varieties will have a mimimal sonic effect. bat and mcintosh are two examples of this.

i have found that many current poroduction tube components are relatively insensitive to changes in tubes.

Mrtennis, all I can say in response to your last post is, bullshit!

Every single tube component from my stable as well as those that I owned in the past benefited from tube rolling. Selected NOS tubes were always my preferences. There ar some nice new stock tubes like JJ or GE 211 among few others but in general, NOS rules. Only my opinion.

P.S
I spoke to more then few designers and in all cases the NOS were recommended and prefered over the new stock. Lowering the production costs and difficulties in finding the right source are just some of the reasons to choose new stock over NOS.

Well designed electronics OUGHT TO BE insensitive to minor variations of components, including tubes. Perhaps this design objective is not met in some audio equipment. All things equal, an old tube should be inferior to a new one because of gas infiltration over time. Maybe gassy tubes sound good...more of that tube sound.