Donna,
My two cents, in point form (although interesting, the other long-winded posts are a bit tedious to read).
Your situation:
1) Your current car is 6 years old already, rather large.
2) You will be living in the New Territories, and your child will be studying there also. Note that distances within the NT are, for HK standard, substantial.
3) Where will you/your husband work? On HK island or in Kowloon I presume? Or from home?
Regardless of the above, my suggestion is this:
4) Yes, drive in HK (makes it worth it because of point 2 above)
5) Do not import your car here. It is too much hassle, is costly, and if you don't mind me saying, your car is not exactly new, so unless you are keeping it for sentimental reasons, get another car here in HK. But be careful if you are thinking about second hand (I suggest a new thread to discuss this if this is what you are going for).
6) Drive within the NT, and between NT and town. If you are spending a day say, shopping in Causeway Bay and then having tea in Central etc., I would leave your car at an MTR station somewhere between your home and town, and take public transport from there (unless you are going to buy something bulky).
C'est tout.