People always say stuff like this, but I think quite the opposite.
Buffet, and people like him (Gates, Jobs, Welch, etc...), while great businesspeople are used to being able to say something and everyone jumps. In business, everyone is working together to make the company more money. With some exceptions, you can create an incentive structure that rewards that.
Government, in the US at least, is very different. Buffet would be dealing with people, congress, who will certainly not jump when he says something. In fact they'll often make themselves completely unavailable. He'll be in a situation where people will actually do things that harm the country if they could remove Buffet from office (to get someone from their party in office). In government, you don't negotiate in good faith.
And Buffet wouldn't be able to fire anyone in congress. I suspect one of the first things Buffet would say after working with congress is, "I'd fire half of these bozos if they worked for me!" Unfortunately, these are the people who will decide what legislation lands on his desk.
I feel like gang leaders are the people who best understand what it would be like to be President.
Definitely. He might not be able to buy the whole thing, but as long as he substantially drives up the cost of a Congressman, that's a step forward. A couple hundred grand (and 10 million in lobbying money) gets you billions of benefits, which is way too cheap.