Perham,
I've tried cases in front of judges who had courtroom experience and some who did not. Within five minutes you can tell if the judge has courtroom experience, and it's scary when you realize that he doesn't. It is more than about "managing a courtroom." It is also about interpreting the law.
With respect to the appellate aspect of your question if you're appointing a trial judge, he should have trial experience. If you're appointing an appellate court judge, he could have either trial or appellate court experience.
Yes, the learning curve is steep. A judge is going to have to resolve disputes dealing with procedure and evidence - stuff you're really only going to learn by doing, not just studying. He's going to hear strong arguments from lawyers from both sides. He's going to need to be able to tell who's right and who's wrong. That's often a difficult call, even if the judge has courtroom experience and has dealt with similar issues in his own practice.
It's tough enough to have to preside over cases involving areas of practice you don't know. For example, I could preside over a personal injury with no problem, but make me preside over an intellectual property case or a water rights case, and it would take a lot of effort. If in addition to that I wasn't an expert in procedure and evidence, I'd be thoroughly lost. It would be an injustice to the parties.
What are the consequences of getting it wrong? Well, it can be grounds for reversal on appeal, which drags the cases out for years and costs both parties huge money in attorney's fees. Furthermore, if the appellate court orders a new trial, you're looking at a big waste of judicial resources and a backlogged court docket.
Set your politics aside for a minute. Do you really question this? Would you want a doctor who had never cut on somebody in his life to perform brain surgery on you? Probably not. You don't want a judge who's never been in a courtroom presiding over your case for the same reason.