To the limit, the existence of F1 itself is condemnable while people live at slums - here in SP, at Cape Town or Bombay. Discussing if the race is held 100 meters or 10000 kilometers from the nearest slum his hypocrite IMO.
From the point of view of the people living there it's a great opportunity to make money renting parking space, selling beer and renting their roofs for people to look into the track.
I agree with you, hiding this poverty will hardly improve it, and its part of the character of Interlagos, is an old track with 70 years since it's first race, and the city developed around it in that part, maybe for the same reason they build the track there (low land value) it attracted poor people, I don't know the exact history of the location... but in some parts it looks really ugly, and unfortunately now looks to late to solve that.
but I think it's a delicate situation, improving the surroundings is very hard, the track also doesn't have that much more of space for new facilities, and who will make the investments? the biggest one was the track resurface in 2007 I think, it worked, but apart from that things looks to be moving slowly and without much investment, also the owner of it (city of São Paulo?) makes things more complicated, since they have so many different priorities, but I'm sure they can see the importance of the GP and make some effort.
as for Jacarepaguá it was destroyed, rests of it are still being used, but it's impossible to repair it to F1 level, and these rests will be destroyed soon, they are promising in Rio de Janeiro a new track, and I read somewhere that they see this discontentment of Ecclestone with Interlagos like a good opportunity.. but I doubt they will come with anything decent soon.
as for the blog with the idea to use some of the old track parts:
http://interlagosantigo.blogspot.com/