I don't know how well the rank reflects a poster's trustworthiness or experience. Plenty of 3-5 star members give incorrect or misleading replies, and plenty of newbies actually read & understand the Terms of Service and are thus well equipped to answer questions in the forum. It just depends.
The "better" option is a karma or reputation system in which your reputation or karma score is determined by how many positive votes you have from other members. However, reputation systems are usually abused/misused, and many posters here are not experienced enough with forums to understand the process & concept.
It seems to me that the best solution here is to just remove the rank, and maybe the post count as well. We do have an "award" system which we could hand out more liberally to the quality posters; that's tougher to manage but probably the most reliable way to distinguish posters.