The year 2008 demonstrated a lot of volatility in the financial markets. How does this affect stamp values? Not much.
Stamp values have traditionally remained unchanged or shown slow and steady growth over a long period of time given normal market conditions. That last point is important. Yes, some people got burnt in the early 1980s when the stamp market went bust after seeing abnormally large increases in value for certain items like a mint set of Zeppelins, Scott #C13-15. That was when the market was influenced by outside forces. There have been other stamp market anomalies, but they are few and far between.
The prices for common and cheap stamps have remained relatively unchanged over the years when adjusted for inflation. The prices for rare stamps in sound condition have shown steady growth over the years.
As the stock market bounces wildly from one extreme to another, you may find comfort in knowing that your stamp values are not in decline. A stamp worth $20 today will probably be worth at least $20 in the years to come.
When you sell your stamps, you may lose some money. Not because the market for stamps has declined. Not because the price has declined. It’s because the value of your stamps has not changed significantly since you bought them. If you spent $1000 on your collection today and in a few years a dealer expects to sell it for that same $1000 price, the dealer’s offer will be less than $1000 in order to make a profit.
I can think of many things that you can put money into and have nothing to show for it in the end. The money you put into your stamps will have some value when it’s time to dispose of them. Stamps maintain their value over time.