Purely anecdotally, but I can think of many friends and relatives who have gone to burning man in the past and are nowhere near the top 2-5%. Last I checked, my dear sister (a self described burner) is living out of a van and selling jewelry at concerts/shows to make a small income.
Also anecdotally, those same burners have mentioned that they are less and less interested in going to burning man based on their recent (negative) experiences in the last 1-2 years and are doing more burner-like things locally.
Your perception is wrong. Every year they do a census. Of the people who filled out the survey most earn under 100k a year, with the average being around $40k. To be 5% of the US you need to be earning 188k a year.
Yes. Anecdotally, the people I know of who do go to Burning Man are either techies or lawyers with upper-middle class income with liberal/progressive ideas or grad students whose socio-economic circumstances are well off enough to allow them to pursue graduate education in the first place.
Also anecdotally, those same burners have mentioned that they are less and less interested in going to burning man based on their recent (negative) experiences in the last 1-2 years and are doing more burner-like things locally.