In chapter 3, Nick Carraway attends one of Jay Gatsby's magnificent summer parties and sits down at a crowded table with Jordan Baker. Nick then comments on the atmosphere of the party by saying,

Instead of rambling, this party had preserved a dignified homogeneity, and assumed to itself the function of representing the staid nobility of the country-side—East Egg condescending to West Egg, and carefully on guard against its spectroscopic gayety. (34)

Nick is commenting on the "dignified" mood of the party, which resembles a serious, modest atmosphere, instead of the typical "rambling" and rowdy environment of an extravagant party. As Gatsby lives in the West Egg and the majority of the people attending his party are products of "new money"; as a result, Gatsby and his guests are conscious of behaving in a dignified manner to avoid being negatively stereotyped by the East Egg citizens. The West Egg citizens are essentially putting on airs to impress the East Egg citizens, who come from "old money." The West Egg citizens want to avoid being ridiculed and categorized as wild, disreputable citizens, who are not civilized like the wealthy people of the East Egg. In order to avoid condescending glances from East Egg citizens, Gatsby's guests behave in a dignified, appropriate manner.

One idea expressed here is that the party-goers are essentially all the same. "Homogeneity" suggests that this is not a mixed group, but a singular and representative collection of people who all stand for the same thing. Set as a contrary to the "spectroscopic" nature of the other Egg, this party does not cover the spectrum but, rather, is concentrated in one band of the social spectrum. 

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This passage does not offer good evidence regarding the materialism of the people at the party, but it does offer evidence relating to the high value placed on social status.