Peter Brown discusses this in the late Roman and early medieval periods, in his recent book Through the Eye of a Needle (2012).

He argues that, in the late Roman Empire, wealth was desirable because it allowed people to enter government office, and because it allowed for public patronage. Government officials had certain legal privileges (such as immunity from public beating, if they were convicted of a crime), but entering government office required a certain level of wealth. Once government office was attained, there was an expectation that the individual would use their financial resources to fund various public projects, such as maintaining civic buildings, throwing public festivals, funding the grain dole (a welfare program available to long-term residents of many cities). So wealth was a means of attaining a privileged legal status, and a tool for maintaining that status by spending your money on your local city in order to fulfill the requirements of your office, act that part of rich patron, and keep everyone under you from rioting.

With the rise of Christianity to prominence, more and more elites began giving their money to the church (encouraged, in part, by many bishops' call to 'store up their treasures in heaven' instead of spending them on 'pagan' festivals). This money, given to the church, was used to build churches and sometimes enrich the clergy, but also to fund enormous charity projects that fed the urban poor (many of whom had been of too low a social status to get any help before the coming of Christianity - see Brown, Power and Persuasion for a discussion of urban poverty and the church).

This is not to say, of course, that Roman elites didn't also spend a lot of money on luxury goods. They did that too.