The psychological research on this is pretty clear (sorry no refs to hand). Below a threshold of income, happiness & material wealth are pretty tightly correlated. Above that threshold, however, the correlation drops rapidly to zero. What that threshold is is open to question - I believe some posit that the threshold is at subsistence level, others maintain its higher, perhaps higher even than median income levels. And of course, Matthieu Ricard, while he is provided with clothing & food, as a monk probably has no income or possessions (other than, traditionally, robes, begging bowls & a few ritual items).