Having taken the plunge myself about 5 months ago I can offer my perspectives on car ownership in HK.
First issue to consider is how useful a car might be to you. Driving into the city (Central, Admiralty, Causeway Bay, Tsim Sha Tsui, Jordan, etc.) is anything but pleasant due to general traffic congestion and confusing street layout with lots of one way streets.
However, what a car would do is enable you to live out in the far corners of HK where living conditions are better than in the high density population centres, but where public transportation is also less convenient.
If you are living right on top of public transportation the only real use of a car would be to go to the above mentioned far corners of HK for recreation on weekends. Also the feeling of driving on your own is a nice change of pace from public transportation every now and then.
Public transportation in HK is plentiful, affordable, and reliable. Parking is NOT, especially in the commercial centres. In Causeway Bay where I work, a full day's parking can easily set you back around $200. Be aware that free parking is not necessarily included with your accomodation, so you might have to pay a monthly parking fee for your home parking as well. Also, there are tunnel fees that need to be paid whenever you use one of the many tunnels around HK, especially the three harbour tunnels.
Apart from that I found the process of buying the car reasonably easy and affordable. Fuel can seem expensive depending on where you are from, but you will not be driving long distances anyway, so a full tank will last you for a while.
In conclusion, most people in HK would easily be able to get by without a car, so it would be a luxury rather than a necessity. So better wait and see how you feel about your situation when you get here and make your decision then.