Most hardcover books from the 19th Century are worth less than they were fifty years ago, while a very small percentage of them have skyrocketed. I expect comics will follow the same pattern.
A 1970s Charlton and a 1990s Marvel will both be fairly worthless while a small group is highly desirable. When The Avengers have published some 3,000 issues and it is impossible to collect full runs, does anyone really think Volume 1, issue 153 is going to sell for much more than Volume 2, issue 37 because one is fifteen years older than the other?