On January 16th 2017, a copy of Amazing Fantasy #15, the first appearance of Spider-Man, in CGC 9.2 condition with off white pages sold for a record breaking (for this grade) $460,000 on Comic Link. A CGC 9.4 copy sold February of 2016 went for $454,100. Prices for high end AF15 have been climbing steadily since 2011, when a 9.6 sold for $1.1 million. AF15 is always in demand, and seeing as how only 11 out of 2,627 copies have been within the near mint tier, this will only increase interest in this book.
Comic Link President, Josh Nathanson, had this to say;
"Amazing Fantasy #15 remains the undisputed Holy Grail of the Silver Age for most collectors. Spider-Man is the single most popular Marvel character and his first appearance from 1962 continues to be in incredible demand. It really demonstrates the tremendous investment potential that vintage comic books like this can have when you consider that in less than a year, this CGC 9.2 example outsold a CGC 9.4 that had previously set a record for that grade level. Amazing Spider-Man is the most collected title in the industry and no collection is complete without the book that started it all."
So what does this mean for lower graded books? Well, they're still good investment pieces. AF15 is a holy grail in the Silver Age collectors market, and now would probably be the right time to invest in a copy, seeing as how most people will be priced out of the high end copies. Recently a CGC 1.0 copy on eBay sold for $7,500, and prices are only climbing from there for higher graded books.
Good luck and happy collecting.