1) Agreed the roads are terrible in California
The other states I've driven in (FL, WA, NV) the roads are way better although still made of that rough concrete rather than tarmac, presumably because of the heat.
2) Yup, plus I think it's the mentality that they are so used to driving long distances and driving on freeways that there is just no point in blasting around everywhere when you can get on freeway then stick it on cruise control for however many miles until you reach your off-ramp.
3/4) Maybe because they are normally bottom-spec engines combined with bottom-spec slushboxes in the hire cars but most of the hire cars I've driven have utter crap gearboxes with, as you say, a very noticeable delay in shifting.
Weather is epic in SoCal right now, shaping up to be a scorcher of a weekend