If it helps at all, another data point (not quite answers to your questions):

• I'm a complete SI outsider. My exposure to it is entirely indirectly through Less Wrong, which from time to time seems to function as a PR/fundraising/visibility tool for SI.
• I have no particular opinion about SI's arrogance or non-arrogance as an organization, or EY's arrogance or non-arrogance as an individual. They certainly don't demonstrate humility, nor do they claim to, but there's a wide middle ground between the two.
• I doubt I would be noticeably more likely to donate money, or to encourage others to donate money, if SI convinced me that it was now 50% less arrogant than it was in 2011.
• One thing that significantly lowers my likelihood of donating to SI is my estimate that the expected value of SI's work is negligible, and that the increase/decrease in that EV based on my donations is even more so. It's not clear what SI can really do to increase my EV-of-donating, though.
• Similar to the comment you quote, someone's boasts:accomplishments ratio is directly proportional to my estimate that they are crackpots. OTOH, I find it likely that without the boasting and related monkey dynamics, SI would not receive the funding it has today, so it's not clear that adopting a less boastful stance is actually a good idea from SI's perspective. (I'm taking as given that SI wants to continue to exist and to increase its funding.)
• Just to be clear what I mean by "boasts," here... throughout the sequences EY frequently presents himself as possessing the intellectual horsepower and insight to transform the world in "impossible" ways and holding back from doing so only because he possesses the unusual wisdom to realize that doing so is immoral. I don't think that much is at all controversial, but if you really want specific instances I might be motivated to go back through and find some. (Probably not, though.)