I have to admit I'm not exactly well read in ADD research, but, what my uneducated outlook on it is that some people are just skattered/inattentive and usually stimulants in the right dose can bring us to normal concentration, but at the cost of overclocking your brain.
It's kinda like overclocking a PC, there are costs. Big ones.
It isn't magic. Last night I slept like ****, and adderall isn't doing **** for me today. Can't feel it, can't concentrate, nothin'. But if I get a good nights sleep its very effective. Also having a good diet is very important, like you said. This helps so much and is so important.
Then again, I really have no idea what I'm talking about other than personal experience. The science of the stimulants makes no sense to me, and I while I'm interested, I've never found someone who could explain to me "adderall" and how it works. Even wikipedia confuses me on this one.