Luxury beliefs is a good concept. It's more than burning money, since it requires one to know what the latest "correct" beliefs are, and it's really rather like fashion in clothes. Just as fashion requires wearing ugly (or at least not the best) clothes, so luxury beliefs require assenting to false opinions. Luxury beliefs also have a strong element of proving devotion to the group, since you have to assent to things everybody knows are false. It's rather like communism that way--- the more outrageous the belief members of the group are required to hold, the better for smoking out dissenters. Maybe there *is* something new to model there, in the bayesian persuasion style, as to how a leader would design beliefs to be outrageous enough to get the optimal amount of information extracted about the loyalty of group members. Another aspect is how luxury beliefs very often aren't "true beliefs", in the sense that people proclaim them but don't run their lives as if they thought they were true. The liberal who is pro-gay but outraged if his son shows interest in homosexuality would be an example. Charles Murray pointed out in Coming Apart how the Establishment proclaims moral laxity, but is actually quite staid in its morals as far as drugs, and family stability. That can happen because for virtue signalling, the signal of declaring a belief is strong enough, and there's no need to push people further towards acting on that belief in their own lives. It's about politics, in the Greek sense.
A luxury belief that all members believed anyway would not be strong enough to signal group loyalty. People would still individualistically say they believed it. To signal group loyalty, the belief has to be one with which the members disagree, so they can be tested as to which they value more, the truth or their group membership. There can also be beliefs about which the person has no opinion and would be willing to agree to either side of the question. Those are useful for showing how smart the person is-- how quickly they can identify the belief de jour. This is the style model.
One can imagine a luxury belief either being created by a leader, or arising from the crowd. If it is created by a leader, then it will be designed carefully to smoke out dissenters. If it is created from the crowd, it has other motivations probably. It might be to catch attention, if the aim is simply to influence the crowd (glory). Or, it might be a belief which the creator actually holds, and wants to see the group implement. Or, it might be defensive, a way for the creator to signal that he values group membership above all else.
Especially if the motive defensive, a bubble could arise. If the first person says, defensively, "Chairman Mao has an IQ of 150!", the second person's defensive claim has to be "No: Mao's IQ is 155," etc.
The Cultural Revolution in China might be useful in thinking about this. There, Mao trapped his rivals for party leadership into disagreeing with unreasonable beliefs that seemingly arose from the crowd. He did not express his own opinion publicly until they had spoken. Dr. Li's memoir, The Private Life of Chairman Mao (1994) has many details of this.