I've never had a problem south of 23rd and on the E/W fringes. Midtown is a nightmare. Taking away the 2 hour meters was a fuck up.
If you have a weekend place a car is pretty handy to have. If you just use it occasionally probably not worth it by the time you add up car payment, ins, gas, maintenance and garage compared to a rental or Zip Car.
There is another consideration: namely the time it takes to retrieve your car. Many people keep their cars a fair distance from their apts to save on monthly fees. I have a friend who lives in Chelsea and drives to his upstate place every weekend. It takes him at least 60, sometimes 90 minutes to get on the road. Call for car day before. Travel the 20 blocks to the garage. Wait along with everyone else for them to retrieve your car. Drive back to his apt and where he looks for street parking so he can load up the car with whatever he wants to bring upstate. Leave the city and wait in the tunnel traffic. Repeat when coming home.