"Money can't buy happiness"
To a certain point, this phrase is false. Countries with higher GDPs per capita are generally happier, but the correlation once GDP/capita exceeds 20K/year is minimal.
How Much Money do we Really Need?
(See also Prioritizing)
Whenever you make a major purchase, you should consider how the emotional value of the purchase would compare to the monetary value. Say you've saved $20,000 over a long period of time. What will make you happier - buying a new car, or buying a used car and donating $1000 to ten different charities, and knowing you've made a positive difference in the world?