According to professor of psychology Sonja Lyubomirsky, author of "The How of Happiness," people in general have a genetic propensity toward feeling good that determines about half their happiness. Another 40% is influenced by how you spend your time.
Why? You quickly get used to money and things. Activities, on the other hand, are fleeting and endlessly variable, which means you don't get so jaded about them. So stop glowering over the size of your 401(k) balance and go do something.
Run a 10K. Learn to play the trombone. Happiness is not something to acquire and save up; it's something you pursue.