I would rather that they simply were not allowed conflicts of interest during and after office. No joining companies lobbying for the industry you were supposedly regulating when in office. ETC.
Take a look at Aspartame controversies. In essence the US Attorney charged with opening a grand jury into their research withdrew and took a job working for Searle, manufacturers of Aspartame. The Grand Jury never occurred. A few years later the FDA Commissioner who gave Aspartame the green light went on to work for their PR company. To this day people don't trust Aspartame even though (debatably) the research shows it's safe.
So even perceived conflicts of interest can adversely affect public perspectives on the objectivity of scientific research. That's not good in a democracy.
http://en.wikipedia.org/wiki/Aspartame#Safety_and_approval_c...