This is a tough situation that a lot of people face. My mom will probably put me in a similar situation one day. However, while she hasn't always made the best financial decisions, most of her troubles stem from medical problems over the past 10 years and the resultant inability to keep steady employment, compounded with the fact that she stayed home with me prior to divorcing my dad and had a hard time re-entering the workforce with a salary similar to what she was earning before. So in this case, I do feel compelled to help her.
In your situation though, where this set of parents obviously won't be financially destitute, I would be much more hesitant to help them. Don't think I would chip in until they have cut the excess spending from their budget. If they made all the changes you suggested (downsize their home, sell the 2nd home, stop waisting money on fancy dinners) and STILL needed help, then I would re-consider. However, it sounds like that wouldn't be the case, as they already have pensions and social security.