9/11 was 11 years ago!
NYC continues to have an influx of upper-income residents while, yes, plenty of illegals too. Look at real estate prices—purchase and rental—in NYC and the city is doing very well, even while managing above average unemployment largely due to strains in the financial sector.
Also, NYC continues to draw young talent nationwide that often ends up settling in the tri-state region when it comes to raising a family. (Though more are staying in Manhattan and Brooklyn all the time.)
I think some areas of NYC are better off than others, but on the whole it is not doing well. I live a few miles from a mall that was built in the NJ Meadowlands to cater to NYC shoppers (we have a lower sales tax). This thing has an indoor ski slope and all; it was finished a few years ago, and it has never opened. It is very eerie to stand outside it; a brand-new, finished mall, less than 5 miles from Manhattan, and it never opened.
For something more recent than 11 years ago, remember Governor Paterson and Commissar Bloomberg insisting the banks that received bailouts still be permitted to pay bonuses?
They very frankly stated that the state of NY, as well as the city (which has its own income tax), were completely dependent on the taxes from those bonuses for their budgets. After 9/11, when the city was asked how they would replace the 343 firefighters that died, their response was: we won’t. The city is in bad shape, and while you mention people moving their, I can’t imagine what they are doing for work.