convince me SA is the place to be!
Dude, come on. Convince yourself
Answers to your Q's:
Rocklands in July/August? - yes that's the perfect time.
Scene at the campsite? - like what a bunch of people dancing to a live band? I'm sure you'll find a couple other boulderers/climbers to bouldering/climb with.
Survive w/o car? - yes, once your there you don't need
a car - but it's advisable, otherwise there is bouldering in walking distance.
Cape Town climbing? yes there loads, if you look on the internet I'm sure you see some.