A Canadian law student writes in:
You've identified one of the causes of wrongful convictions, but it's also the most expensive one to fix, and probably not one of the most important. I'm a law student in Canada, and recently finished a course on wrongful convictions. We generally have better funding for defence lawyers here, but there have still been wrongful convictions in cases involving some of the best defence lawyers in the province.
The Innocence Project has identified the causes of some of the wrongful convictions they have exposed. In 130 cases, mistaken eyewitness identification was a factor in 101 (the next most common was false confessions, which were a factor in 35). Most wrongful convictions happen with a competent defence lawyer and an ethical prosecutor. But that won't be much help to a wrongfully accused person in a case with a false confession and mistaken eyewitness identification.
Don't get me wrong, insufficient funding for public defenders is a huge problem, but there are some even easier solutions to bigger problems. One change, which has been adopted already in many parts of Canada, is showing photo line-ups to accused one photograph at a time, which reduces the chance of a witness guessing the photo that looks most like the person they remember. Wrongful confessions are less likely to occur if police videotape interrogations (all of it, not just after a suspect starts confessing). Those are just two easy, and cheap, steps that would reduce the danger of wrongful convictions.