I bow to Colin on his assertion that there are in fact 5 settings for the lights; my Lexus dealer explicitly told me there were three however, so either there is a UK/US difference or the dealer is wrong. However, whatever they did, my lights now come on a bit more sensibly.
As to the boot opening, no, I've never opened it inadvertantly, and I find it easier to just press it quickly when I have an armful of shopping. My boot, however, does not fly open (or even move at all - it just clicks free and then it can be lifted. You'd never know it was open at all unles you tried to lift it.
I don't know whether that's the springs or whether it's behaviour by design on the GS.