When was you in Mumbai last time? I have been there too (before 9-11), and was quite disappointed.. after witnessing state of affairs.
Especially the airport... which sucked the most and slums... surroundings airport sucked equally.
12 years is a lot of time for change. Most of the new cities that China has built have come up in the last 10 years. If you had gone there 10 years ago , you would have seen nothing but fields, grass and slums.
If you want an example from India. Take Gurgaon , which 10 years ago was a grassland/wasteland with lawlessness ,slums etc. It was practically uninhabited except for perhaps a few odd villages here and there where you would probably get mugged if you went late at night.
Here is what it is today.
Gurgaon Cityscapes - Page 102 - SkyscraperCity
It can compete with some of the best cities in the world. Some things don't change though. Now if you there late at night , you would probably be mugged and then murdered ,or raped , if you are a girl. Money has made people even more greedy.
If a new city can be made in 10 years , then obviously a financial capital like Mumbai can be drastically changed.