So what were the valuable European colonies?
France had major support from its overseas colonies during WWI. Britain had even more support from its colonies and ex-colonies in WWII.
Without that support, neither France nor Britain would likely exist as independent nations or empires in the modern world. At the very best, they would be vassals of Imperial Germany or the Greater German Reich.
I'd say that France and Britain, their colonies paid off handsomely.
Portugal, Spain, the Netherlands, Belgium, and Germany didn't get that kind of payback from their overseas possessions, but the first three realized a comfortable income from them for a trivial amount of cash outlay, so I'd have to say they were wins too. I'd have to do some research on Belgium and Germany, but I'd guess they probably did little better than breaking even.