Living in CWB, my wife definitely needs the car more than I do. Maybe living close-in to Sai Kung it would have been different, bus she generally drives to Hang Hau every day for the grocery shopping and for going into "town" on the MTR (Park & Ride), and doing that from Sai Kung would have been more difficult, given the greater distance from the MTR and the traffic problems.
Some people find CWB very isolating, especially if you're not working every day. It is just a residential area, after all, so you would need to find your "community" somewhere else. Creating a new network takes months and months...
If you're the kind of person who likes your greenery and your open space, the Mid-levels are never going to do it for you. There are no parks like the ones in London. (Yes, there are a few parks--they're just not at all like the ones in London!) We lived well out of Central London so that we could have a nice garden, etc., and I'd never live in NYC for the same reason I had no interest in living in most places in Hong Kong. (DB was a non-starter for me, but mainly due to my being a petrolhead...)
Definitely don't decide before you get here, though.