No, what Kaka did deserves praise, no need denying it, as much as one dislikes him or Milan.
Yes, maybe he wouldn't have said no if it was a team bigger than Man City and yes, he's already earning more money than 99.9999% of the football players in the world, but saying no to twice bigger salary does say that there is still more than the financial aspect in football, for some players football is much more than business, and it does say that there are still players who care about the jersey more than about money.