Since at least 1900, people have touted stamps as an investment. The first United States stamp to be speculated in was the 5c 1847 (Scott #1) which was the subject of a market push in the early 1900s. A group of speculators figured that they could push up the price of this stamp and began by offering to buy all that they could for $1 each. They soon ran out of money and prices fell back to the 70c or so level that had prevailed for the previous decade. Still by today’s standards these prices seem very cheap, and with a nice US #1 selling today for about $180, even with inflation those speculators would have made out pretty well indeed. All philatelic investments are really a speculation, even the most tried and true of philatelic specialties. In the end all philatelic material will either go up or down depending on the long term health of our hobby and the number of people who collect stamps. No matter what you buy, no matter whose collection it was in before you and no matter how blue ribbon its pedigree, if there is not an active body of collectors wanting it the price will go down.
In the last forty years, the classics that old timers cut their teeth on have languished in price while newer issues from emerging countries have risen rapidly. Forty years ago one of the great classics of philately, the double Geneva of Switzerland, cost $75000 to buy. It was considered probably the safest philatelic investment only it has performed horribly. Today you can buy one for $20000 and when you figure the value of money over that period the investment has been a poor one. The problem with investing is that at any given time it is very hard to see anything except current trends. Today, classic stamps look to be a bad investment and emerging nations stamps look to continue to grow rapidly. But an earthquake or political upheaval could change all that and then the owners of classic will look like the smart ones.