I am not convinced that the rationality level has perceptibly increased over the years, judging from the comment threads then and now

My estimation is a decrease, mostly due to dilution of the seed polulation from Eliezer-era OvercomingBias. This isn't necessarily a bad thing. Remaining a bastion of the already reasonably rational wouldn't have made lesswrong particularly useful. I'm willing to put up with a somewhat lower standard if it benefits others.