My uncle has lived in Manhattan for the past 15-20 years and I can say its a great city. There is a ton to do and everything is larger than life. I have been going there for as long as I can remember to visit him, also my girlfriend and I will go when he is out of town on occasion. If your going to Tiffany’s or Bloomingdale’s be prepared to spend $$$$$$.
I personally feel the city is a safe place… of course you have your neighborhoods like everywhere else. I feel safe walking down the road at 2-3am by myself, there are police everywhere. I also wouldn’t worry about your ride getting stolen, if you get a decent hotel in the city, they will have a parking garage. Staying in NJ would be ok I guess, but I feel you really cannot take full advantage of the city night life. I guess it all depends on what kind of budget you are going on. Sure you are going to spend more on a hotel in the city… but at the same time, the subway and cab fees have gone up a lot, that all adds up. Your better off defiantly staying in the city, it takes hours to get in and out of the city and its $$ for a cab, plus tolls, etc…
Also… if possible… leave Friday… stay the extra day, you really cannot do much in that time period, if you can’t thats fine… but you will appreciate the extra day in the city.