As you have probably discovered already, the walled city are long gone and gave way to a large modern park so as an independent area/entity the walled city has long ceased to exist
The area around it, which is the larger Kowloon City, is going through a bit of a revival at the moment because the closure of the old VHHH (Kai Tak) means that it (located directly outside the threshold of runway 13) is now free from the old height restriction rule (translating to roughly 6 storeys in height which was also true for the Kowloon walled city). A lot of 30-40 storeys brand new apartment blocks have now replaced some of the old buildings which were of similar style to those found in the Kowloon walled city.
If it is just the building styles which is of interest, I can gladly inform that many parts of Hong Kong (mainly in Kowloon) still has this type of buildings, which I believe are dated from the 1940s - 1950s. They can still be found in areas such as Kowloon City, Mongkok and Shum Shui Po (they have subway stations of the same name). The people who live there tend to be the elderly and the poor, which is what you'd expect to see in the Kowloon walled city when it existed (minus the prostitution and the triad groups). However, in recent years the government there has relaxed laws relating to urban redevelopment for the entire city and these type of buildings are rapidly being demolished as they are the oldest and all of them are very ill-kept. If you look at the outer walls and the build up of black soot over their once light-coloured paint you will get the idea. My impression is that all of them will be gone in say 20 years time.