- win so you can do stuff
- do stuff so you can win
It's an attractive idea - if there's some percentage of Congress that isn't up for re-election, they might be less inhibited, and therefore more likely to support things that, for instance, their district doesn't support but that are good for the country as a whole. They might be more capable of standing up for things that aren't popular, but still The Right Thing To Do if they don't have to worry that they can't explain themselves well enough to get re-elected. In a highly-polarized political landscape, bipartisanship might be easier if there was less election pressure. Furthermore, if there's not a career in it, you might attract a different breed of Congressperson that isn't so winning-obsessed.
But there are potential drawbacks too. Some Congresspeople get better at their jobs as time goes on. Boot them after 6 years and the game drastically changes in a way that I don't think can be accurately predicted. Let them stay for 12 years and you've pretty much equaled the average political lifespan anyway. And term limits really just make the individual less inhibited - not necessarily less inhibited to be more bipartisan, or to stand for The Right Thing To Do. People could, conceivably, stop caring about their jobs, stop bothering to reach out to the other side, and stand up for positions that in fact are The Wrong Thing To Do. Plus it still doesn't affect parochialism - and that's the biggest challenge in federal governance. How do you get a Congressman from rural Oklahoma to want to pass legislation that only costs his constituents money while primarily only benefitting, say, urban areas? And what do term limits really do to limit the role of money in politics?
Bottom line: I'm not convinced. Maybe term limits could be part of an overall package of reforms, but they're no silver bullet.