Yeah he probably spends his money poorly, but I don't think you realize how hard it would be being a professional athlete. Think of the job you had, think if you had to always be paying people to train you, paying for airline tickets, paying for healthcare, supplements, equipment, hotels etc. etc.
Sure Leben was an idiot with his money, but he probably wasn't as bad as most basketball players who piss it all away on luxury items. The cost of training for mma plus taxes would make it tough to live the lifestyle of a professional athlete with the money they make. It costs a lot to do everything involved with training.