I guess to me prestige is secondary to actually doing the job. After all with the congressman's connections he or she can continue to have an impact afterwards. Look at retired US presidents and vice presidents who want to continue to make a difference! Sometimes it's even easier and more pleasant for them once they're out of office.
People also say that regulators are captured by the industry via opportunities they get in a revolving door. They are offered cushy positions at the industry after they stop being politicians, in exchange for favorable votes. I could see this as possibly being a bigger motivator than re election.
Maybe there should be some consequences to not voting according to the policies you ran on. Buy in any case, if most politicians are awayed by lobbying, then being one politician who isn't won't make a huge difference.
