I disagree that credentials are the answer. Weighing with credentials doesn't scale broadly, which is what is needed here, and in fact may aggravate the problem when the expert has a bad day or their authority is applied to inappropriate subjects.

A better solution than "giving the smarter people a louder voice" would be to "give the louder people a smarter voice."

My suggestion below is to add a good way to discreetly provide feedback. Encourage people to send messages to you about what they think of your post, with the goal of encouraging everyone to improve the quality of their posting, and also to be more thoughtful about up/down voting.