The question- what makes a 1st full appearance more valuable (IH181)(( where u at slym)), or a cameo more valuable (Jimmy Olsen #134), or an Ad appearance more valuable (Gobbledygook #1), or a preview appearance more valuable (DCP #26), or a promotional magazine more valuable (San Diego Comic-Con Comics #2) - Is simply answered by these words: The Market
If we're borrowing examples from other industries, I would compare this discussion to an argument that happens daily among music enthusiasts: What makes a record a hit record? Its the market.
Granted, intellectual properties were written and distributed properly to the masses, its now up to the people to decide what they prefer to read, listen or collect..