The best take on that topic I've found is Machiavelli's Discourses on Livy. He did have a tendency to idealize the early pieces but whether he believed Livy's every word or merely pretended to is a little hard to determine. Great stuff.
Yes, the story of Marius and Sulla is a good one and it shows what happens to great men without the humility of godliness. Marius’ reforms were critical, but his thirst for power and inability to tolerate rivals brought havoc to Rome. It’s interesting that once tradition is broken it is very hard to reestablish.
Gresham’s law is true not just of money, but of everything.