Hold on to the book for a while - thats the best advice you can get. In the current book market, most books printed in the last 50 years are not that collectable, with some rare exceptions. However one should also realize that the value of a book in good condition does not normally go down, in fact the price will remain for the most part equal to those of new releases, taking into consideration condition and all that. The other things that add to the value of newer books (again 50 years old or less) are rarity and demand (naturally). I once came across a book of poems, only about twenty years old, cheap paperback printing, that I picked up in a dollar bag and resold for $50. Apparently most copies had been burned in a warehouse fire. Thus it was rare but as far as books go that sort of situation is rare as well. The problem with mass publishing is that the books are, well, printed in mass and there are lots of them. Thus supply, even in out of print books, normally exceeds demand.
Also remember that autographs do not immediately add a lot to the value of a book. Wait until the author (or whomever) dies and their autographs become impossible to get any longer. Then their scrawl has more value.