I want to reduce the rate of employee theft in my company. I'm going to limit their employment to five years, so they can't steal as much. My turnover, training, and inexperience-error costs rise, but I will have less theft!
Come on, man. It's not even close to the same thing. The longer a politician is in place, the more they can wrap their tendrils around all sorts of things. If lobbyists and cronies know a politician has only 4 years before being replaced, they are less likely to make risky deals/bribes, etc.
You're trying to limit the bad behavior of fervent self interest, which typically becomes manifest in money, with the crude tool of a time limit; which limit also applies to the good behavior of fervent public interest. Cap their net worth for a time and you remove the incentive for the former interest and leave unaffected the incentive for the latter interest.
I think capping net worth is a great idea. But again, time limit IS relevant in political appointments, because if it is known that there is no limit, people rush to influence the new "king", and all of the corruption that goes with it. Rather than just saying "well, we only have him for four years".
Personally I think "we only have him for four years" itself creates the rush. But as long as we're not talking about limits so short as four or eight years then I could be persuaded to accept the limits AND a net-worth cap. As for that latter cap, I think it should apply for a goodly period after they leave office, too, for obvious reasons.