Well that's the thing, isn't it. It's easy to glamorize the filthy and dangerous past of New York, and tell war stories and feel that unique pride of survival. But not many people would want to go live in 70s/early 80s New York again. Or even visit it.
Just like no one in Los Angeles wants to go back to the 80s or early 90s and all the murder and chaos and misery. Living through times like that only makes you appreciate better, slightly more peaceful times. I'm not arguing for gentrification, but maybe as you get older and don't want everything you do to be a dangerous or miserable ordeal, you look at things differently.
I think big chunks of New York and Los Angeles were made less dangerous and more pleasant without completely losing their souls. But of course some places did lose their souls, so...
Boston in the '60s-'70s was filth pit (along with the "dirty water" Charles River). There were a few neighborhoods where you felt like a human, but too many where you didn't want to turn the corner, and litter, litter, at every turn. It was as if every Burger King and McDonalds restaurant in the suburbs had been blown up, and all the garbage had landed in Boston. Of course, I was young and my mother was a staunch Irish Christian, so peeing on the sidewalk was a sign of the devil.
The city took its time cleaning itself up, and eventually, with with the help of a verbally bungling now ex-Mayor who is loved and ridiculed at the same time (Thomas Menino; a great man who has done a bunch of great things for Boston, but he just can't express it properly), and today the city is largely a safe place, a clean place, and thanks to The Massachusetts Water Resources Authority (MWRA), you can fall out of a canoe in the Charles River and not have to get a tetanus shot.
In some respects, Boston has lost a bit of its soul (Wally's Jazz Club, a 40s/50/60s bastion of top jazz talent, is now a relic with less interest), but by and large, the regentrification of Boston, Cambridge, and Somerville (my old haunt) has worked, as long as you aren't banking on subsidized housing and somesuch (let's not get political if we can help it). The history is still here, and the tourists were here in the 60s/70s/80s/90s, etc. So, it is was it was, or something like that.