Much like the OP, I had worked on my bikes for many years, but wanted to learn higher level "pro" skills without working at a bike shop. So I attended Barnett's Bicycle Institute (BBI) for 3 weeks in 2011. Week 1 consisted of a Bicycle Assembly and Maintenance coursework with an extra half day of wheel building. Weeks 2 and 3 consisted of Bicycle Repair and Overhaul instruction.

The BBI approach was very objective in order to maintain high standards and ensure a quality product. For example, spoke tension was measured with a tensiometer, not by plucking for tone. Bolts were tightened with a torque wrench to manufacturer specifications, not by feel.
Procedures were performed stepwise in a manner the same way each time using an algorithm-like approach. "Short cuts" were not allowed unless it was by combining steps, never by skipping steps in the algorithm. Speed came only by getting more efficient and quicker with repetition.
Personally, I liked BBI philosophy. My career was in medicine and science, and so I was very comfortable with objectivity, measurement, and standard operating procedures. It's a dependable approach that maintains quality of knowledge and performance among many individuals working at the same place.

Before I chose Barnett, I spoke to several people about both schools and one described the two schools this way: Barnett is about the science of bicycle repair -- United is about the art of bicycle repair.
I think that holds true for Barnett. I have not received training at United Cycling Insitute, but I have heard from several mechanics trained there that they did learn a less objective, less regimented approach that works just fine for them.