Jerry Weinberger of the City Journal, a libertarian occasionally conservative journal on urban affairs, claims in his article "Gentrifying Washington, DC" it does. So he uses an incident on his street in Capital Hill to illustrate his point.
Friendlier? Eh, I don't know. The drug dealers on the corner were friendly. There is a new crew of old guys selling, old as in their 40s looking 50, which makes me appreciate good living and exercise. They pretty much ignore anyone that doesn't look like they're buying and may grumble a greeting if you pass close by, maybe. Cindy (the ex-crackho) is still as friendly as when she was selling herself cheap. The block I used to avoid, has a friendlier vibe. That one is hard to gauge.
More diverse? Yes. First let's define diverse. More than just one type of demographic. Shaw and more specifically the TC had been overwhelmingly African American for at least 70 years. My TC study showed that the area that from 1880-1920 had been diverse wham! became black and kinda stayed that way until the 2nd wave (I think the 1st was in the 80s) of gentrification. And it is that change to have more economic and racial diversity the cries of gentrification get thrown around.