I remember watching a collectible show on tv (not on anymore and can't remember it now) that discussed the lifespan of collectibles.
The basic theory was that generally nostalgic collectibles will start to go up in value when a person is in their late 20's (meaning that right now, collectibles that were around late '80's should be starting to go up in value as collectors enter the market). By your 30's things are really hitting their stride (which would be items from late '70's to early '80's), by your 40's the collectible has peaked in value, and by your 50's people are looking to downsize their collection and generally supply outstrips demand (the example used 10 years ago was Western type memorabilia like Howdy Doody, Bonanza, etc.).
This was 10 years ago and he mentioned if you wanted to make some big bucks in the collectibles market (today), start buying Masters of the Universe, Transformers, and TMNT. I distinctly remember purchasing a mint with tags MOTU luchbox for about $20 (around 10 years ago). I could easily sell it at a profit today.
"The farther we go, the more the ultimate explanation recedes from us, and all we have left is faith."