I've recently enjoyed an article about the pitfalls of design by committee, called "How to Ruin a Web Design — The Design Curve". The author sarcastically writes about the situation of "design by committee" (and has some great charts to "prove" it). The article is humorous, but makes a great point: more time spent or more people involved does not equal better work. The situation can take on external factors and lose the focus of the intended target audience.
In my career this has been proven many times over. The best situation is a reasonable timeline, solid plan of attack, clearly defined goals, and a small group of enthusiastic champions for the project (or better yet, a single champion).