These 4 main neighbourhoods (as well as Hípodromo) make up the 'bubble' where you'll find most foreigners and well-to-do Mexicans residing within Mexico City. 
The tree lined streets are full of cute cafes, high end restaurants, well behaved dogs and remote workers tapping away and it makes for the perfect neighbourhood to base yourself out of.
We've heard numerous times how foreigners moving into the city is 'changing' and 'ruining' the areas - however after speaking with several locals this does not appear to be the case.  Polanco has always been where the wealthiest Mexicans live as it's the most stable part of the city during an earthquake, and Roma Norte has always been home to creatives and well-off locals.  In their opinion - the level of foreigners choosing to also make this their home has not had a negative effect, if anything it has just increased revenue for the district and business owners!
Petty crime does of course still occur here, but you'll notice most people have no issue leaving their iphone and macbook on the table or walking around with headphones in.