...however, very small countries and those which developed postal systems very slowly would of course have heir early stamps carry quite a bit of a premium in many cases.
You would think so but it can be counterintuitive. Many "dead" countries and small countries (population of course) did indeed issue small quantities of stamps at times but very large quantities of stamps for the most part. Some of it has to do with colonization and the "mother" country producing omnibus issues with the only difference being the colonized or controlled countries name and currency, if different, on within the common design.
The other factor is demand. There just are far fewer collectors seeking out smaller countries stamps than there are United States or major European countries stamps.
I was always shocked at the amount of stamps that come along in large lots and collections from countries that most people would need to Google.
The postal history aspect of these geopolitical places is often far more valuable but again the demand is softer than for a dollar value Columbian.
I ooh and ahh over many of the WW items in major auction catalogs because they are so rarely seen and so fascinating. Quite a few though realize shockingly low results given their populations.
I am not a coin collector but it would seem that stamps are a tougher nut to crack in some ways such as the sheer volume of different issues and the fact that they were meant to be used once and discarded for the most part. Stamps are so fragile compared to coinage as well.