The thing is, we all know lots of people and lots of stories. But the research is based on all of our stories- and all the stories we don't know about. Overall, this seems to be true. Maybe not for us individually; but what the research is saying is, if you have to make an informed guess about what will be true for you, well, here it is.
You do come across ppl who get a terrible health scare, and immediately lose the weight/give up the fags. But it's too late then. If they had done the same thing ten years earlier, who knows?
This is the nature of preventative medicine. By definition, you are talking to ppl who aren't ill yet, and might not become ill, about doing something they don't much fancy doing. Even if you can sell the immediate benefits of losing weight or giving up the fags, the long-term stuff seems very remote.
Do you have a duty to your kids? this is typical mum-speak: if I think it is for the benefit of DP or DC I can justify it. Not having a go at you, because I am absolutely just as bad. The fathers I know don't do this, you know: they lose weight or what have you for themselves, not for others. how about doing it because you, personally, deserve it?
As for is it worth it: the honest, sisterly answer is yes, it is worth it. You will feel better, have more fun and be healthier. I woldnt do it all through diet though, as it is a huge pain and a bore. I would take up some regular sport- cycling, perhaps, or swimming, so you don't knacker your knees.