I guess no matter how great the product, the issue is with people. Hardly anybody will keep up writing static content and maintain it so it stays relevant. The best knowledge base is probably a great Q&A system with an active community.

If your current knowledge management system is too empty to your likings don't bother buying a new knowledge management system. It won't help. Instead, give your employees and customers a central place to ask questions and grow a culture that answers them as a first priority. Make that searchable and throw away your knowledge management system...