I was talking today with a friend of mine of how many things we think about all day, and we arrived at the conclusion that too much thinking is a problem in itself. If we were dumber, would we be happier? If instead of thinking of the rice milk, and the granola, and the whole grain rice, and the best school, and the extra curricular activities, and the safe environment, and recycling, and getting the best deals for all insurances/cable/cell phone, and the best career, and, and… and if we just thought less, would this make us happier?
I search the net to see if our hypothesis is correct. I found the best answer at Quora, but since they ask you to create an account to read the answer, I’m copying it here verbatim:
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Compared to research looking at personality and happiness, the relationship between intelligence and happiness has not been studied heavily.
According to the existing psychology research literature, however, the answer seems to be no. Generally, studies have found no relationship between intelligence (as measured by IQ or other tests of cognitive ability) and happiness.
In “Correlates of Avowed Happiness” by Warner Wilson (1967):
The data show quite definitely that
in spite of numerous lay theories to the contrary, happiness and IQ are not related to an appreciable degree
, at least in the student populations studied. The most extensive studies found no relationship (Hartmann, 1934; Watson, 1930; Wilson, 1960). Fellows (1956) reported that the intelligent are less happy; Jasper (1930) and Washburne (1941) reported just the opposite. Several studies (Beckham, 1929; Bradburn & Caplovitz, 1965; Gurin et al., 1960; Inkeles, 1960; Wessman, 1956) showed, however, that those of a lower socioeconomic level avow less happiness. Since relatively low IQ is a characteristic of low economic status, these investigations suggest that intellectual capability may be important when it is low enough to prevent economic success. Those with high IQ, in any case, do not seem to suffer from any special mental distress.
(p. 304) 
More recently, Eysenck (1990, p. 33) suggested that “Despite the fact that it definitely seems preferable to be clever rather than dull, there is very little evidence that intelligence is related in any way to happiness.” 
Note that, as stated above, many of these studies were conducted on college students and therefore not terribly generalizable. It could be the case that intelligent people become unhappy later in life due to the career paths that they choose for themselves.
Studying a Dutch cohort born around 1940, Hartog & Oosterbeek (1998) found a positive relationship between intelligence and happiness that went away after statistically controlling for education. This study actually found that individuals with intermediate range education (not low, not high) were the most healthy, wealthy, and happy.  This study actually makes me wonder whether there might also be an inverted U relationship between intelligence and happiness, where the happiest individuals fall in the middle range of intelligence. It makes me want to go read all of those 1950s and 1960s studies to see whether they were only testing for linear relationships. Anyway…
Looking at trait emotional intelligence, however, tells a different story. Furnham and Petrides (2003) studied cognitive ability, personality (Big 5) factors, and emotional intelligence in relation to happiness. Individuals with high emotional intelligence reported greater happiness. 
 Wilson, W. (1967). Correlates of avowed happiness. Psychological Bulletin, 67, 294-306.
 c.f. page 18 of Furnham, A. & Petrides, K.V. (2003). Trait emotional intelligence and happiness. Social Behavior & Personality, 31, 815-824.
 Hartog, J. & Oosterbeek, H. (1998). Health, wealth and happiness: Why pursue a higher education? Economics of Education Review, 17, 245-256.
 Furnham, A. & Petrides, K.V. (2003). Trait emotional intelligence and happiness.Social Behavior & Personality, 31, 815-824.
— End copy — (and thanks to Elaine C. Smith for the great answer)
Bottom line, being smarter is not a good excuse for being sad or depressed. So find a new one :-).