It is an interesting truism that those who offend the most are also the most easily offended.
Isn't that so very interesting?
The essence of noobness is attitude, not join date.
But there was a substantial amount of time when Showcase #4 was considered the premiere Silver Age book to own. That absolutely shifted in the late 70's, as those who grew up with Spiderman and FF now had the cash to buy them up, but demand has a funny way of changing, even over relatively large measures of time.
Showcase #4, even if it had similar numbers as AF #15, wouldn't likely come down to the price of a, say, Showcase #27 or #34...or maybe not even a #22. There's still a considerable amount of demand.
The interplay between supply and demand isn't always easy to define.