It appears that I may have been doing the right thing in putting together Building Skills in Object-Oriented Design . Expertise is grown through "effortful study" of the material. Experts search through their long-term memory for applicable patterns, based on their study.
The idea of many exercises, each exposing a piece of OO design seems to fit this "effortful study" niche.
The next step is to rewrite parts of the introduction, and change the sales pitch.