jhuffman:

The specter of a jury trial sets the stakes for everyone and does help keep cops and prosecutors honest to a significant degree. No prosecutor can have a losing record in jury trials and expect a long career, so they also have incentives to make deals or to dismiss cases that they don't have the stones to try.

That, however, is a double-edged sword. It also gives the prosecutor a strong incentive to use every dirty trick available to ensure a guilty verdict should the defendant refuse to enter a guilty plea. Since the cops typically have at least some incentive to cooperate with the prosecution, this can stack the deck heavily against a defendant who can't afford a super-capable defense lawyer.

This is especially problematic considering that forensic labs are hardly a paragon of pristine scientific objectivity -- they are run by the cops, after all, and base their work on lots of questionable "science". Moreover, according to the stories I've read from defense lawyers, the truth of police testimony is normally taken for granted by juries, unless the defense can muster overwhelming evidence to the contrary.

Overall, it seems to me that unscrupulous prosecution supported by the police has a very good chance of railroading any defendants who can't actively prove their innocence (and even those often won't be able to pull it off without a very good and very expensive lawyer). Therefore, the net influence of the prosecutors' incentives to win jury trials on the quality of the system is questionable.