If a 707 or a 757 slammed into the World Trade Center, it might be much more damaging than the case of the B-25 bomber that crashed into the Empire State Building.
For one thing, unlike the Empire State Building, which has more heavy concrete, the World Trade Center is made more of steel and glass - this may mean far greater structural damage due to the impact and flying glass shards and debris raining down on the people below. There could be a possibility of toppling if the 707 or the 757 came in at a high enough speed. Both of these planes are larger and heavier than a B-25 bomber, so this means a greater force of impact. I'm no expert on building structure or air crashes, but it would no doubt be far worse than the Empire State Building disaster.
It is very doubtful any passengers or crew would have survived such a grim scenario. Also, there are probably more people per floor in the World Trade Center compared to the Empire State Building, so casualties in the building will likely be much higher.
However, I wouldn't be surprised if the authorities would have a strict exclusion zone preventing any large airplanes, especially commercial airliners, from getting too close to Manhattan, so that there would be no repeat of the Empire State Building crash.
Other large buildings have been crashed into by large airliners, like the El Al 747-200F that crashed into an apartment complex in Amsterdam several years ago.
There was a small Cessna plane that crashed into a hospital in Edmonton, the city where I live. This was in the early 1980s, and did prompt fears about larger planes crashing right in the middle of Edmonton. The hospital sits right underneath the approach path to the City Centre Airport. It was quoted in the news by a member of the city council that "one day a 737 will slam into the hospital, and that will be it".
Edmonton City Centre Airport (formerly the Municipal Airport) did used to have quite a few 737s and BAe 146s flying in and out of there until 1995, when it was closed to most scheduled flights. This airport sits only a few kilometres north of downtown Edmonton, so it is well within the built up areas.
There are risks when you have an airport like Kai Tak(now closed) or Love Field in Dallas, TX served by larger airliners the size of a 737 or larger and sitting well within an urban area. Believe me, it's amazing that Kai Tak has never had a disaster like that, considering that Hong Kong has so many skyscrapers so near the airport - and that Hong Kong is one of the most densely populated cities in the world.