>What I often see in my local election is that 3rd-party candidates are often (not always, but often) very inexperienced, and might have platforms that don't make sense or aren't coherent

This is a symptom of our current system. Anybody who has any ambition in politics will modify some of their positions to fit one of the major two parties. If running for another party wasn't a death sentence, you would see more competent candidates in those parties.