If cholesterol levels are still only a fraction above normal, this might help but in most cases it won't have enough of an effect.
Most cholesterol doesn't come from the diet but is manufactured by the liver at night, which is why statins should be taken at bedtime.
I've been on simvastatin for over 10 years and have not noticed any side effects. I know muscle pains are a common side effect but I haven't experienced any although I do take Co-enzyme Q10 which is supposed to counteract these and is anyway reduced within the body as we age.
As for the link with dementia, who knows! My husband was put on statins when his cholesterol levels were low but the GP wanted it even lower as he had diabetes. I wasn't happy but whether it contributed towards his dementia I don't know as he'd already had Peripheral Artery Disease for some years which was a far more likely cause.
I was considered a high risk of a heart attack as my father died at 56 from one. I also have a shortness of breath though whether this is linked to the heart or to asthma is inconclusive.
I have to say that when I've stopped taking the statins for a week or so after reading such threads as these, I have noticed no difference whatsoever.
All medication is a case of assessing the benefits over the risks.