Definition Of Hi-Value Stamp?

Surely any workable definition has to be a "movable feast" based on the underlying basic postage rate at the time, rather than a fixed concept ("anything over a $1"?) which is only valid for a particular snapshot in time...?

For instance here in Britain a £1 stamp was certainly 'high-value' in the 70's when basic postage was in single figures; but now that a standard 1st class letter is 60p, £1 doesn't seem anything like enough... Also a 'flat rate' doesn't really work for many european countries which don't denominate in 'whole units' but rather in eurocents i.e. 150 cents, not 1,50 euros.

In my mind 'high-value' ought to be "about 5x basic rate" - in the UK at the moment that would be £3+ - which feels about right.

It depends on the era I suppose. Take the 1861s... IMO the 24c, 30c and 90c were the high values of the set.

I have always found "high value stamps" relative to anything above the first-class rate or the old domestic airmail rate in the USA. Now, you have to remember the first stamp issued when I began collecting was the 1967 5-cent Christmas issue. An 8-cent airmail for the centennial of the Alaska Purchase was "pricey" and the $1 Airlift stamp was unobtainable. Today, a 5-cent or 8-cent stamp is a changemaker and the $1 stamp would be far more commonplace.