Stamp collecting doesn't exist in a vacuum. That is to say that what happens in the world affects the prices of and interest in certain stamps.
"What stamps are a good investment?" is a question that frequently comes to me here at About.com Stamps. With the speed in changes in finances and government these days an answer that may be correct today can be wrong tomorrow. Let's take the situation in Greece right now. Should you buy Greek stamps? If you are a collector perhaps you might consider it: surely collections are coming onto the market at bargain prices. And we all know that when supply is on a par with demand the buyer is king. But if you are an investor you might think twice, as continuing turmoil in that country makes your investment risky at best.
But I'm not sure that the stamps collectors acquire in such a scenario will satisfy them in the long run. There is a bit of the carpetbagger feeling to it. You know that feeling if you've ever gotten a great bargain from a dealer because you had superior knowledge concerning an item he underpriced. Some collectors can live with it. Others cannot.