I think there are two parallel discussions in this. For most collectors, I think the interest in 2nd prints as variants often relates to identifiably different features in later editions - like the "Classic" tags on the So Much Fun editions, Marvel's gold ink 2nd prints, and DC's Roman numerals. These distinctions create "variants" that are easily recognized by many collectors, and this awareness allows demand to build in a way that - when combined with relative scarcity - can drive price increases into a feedback loop, where each price increase prompts more collectors to seek these books out.
I think this stands in contrast to the many Batman reprints (for example), where the key differentiating factor is relatively obscure - like the numbers or symbols in the UPC codes, or the copyright dates of internal advertisements. These later prints - while still scarcer variants - lack the widespread "identifiability" that will touch off the collectible feedback loop. There are exceptions, of course - the McFarlane cover of Batman #423 seems to drive some additional attention for the variants of that issue, and there are whole threads here (and elsewhere) trying to sort out the nuances of early TMNT printings.
By and large, my sense is that this holds true...
Just my two cents... I'm interested in other perspectives on this, though...
Great post! (thumbs u Btw, I spent the afternoon Mylaring Copper Bats (350-450), with an eye out for 2nd prints. I was pleased to find none.