As I wrote on another discussion list on RG, I think (I hope) you could find some interesting stuff in
I. Barkana: “Adaptive Control? But it’s so simple! A Tribute to the Efficiency, Simplicity and Beauty of Adaptive Control,” Journal of Intelligent and Robotic Systems, 2015 (Published On-Line) DOI 10.1007/s10846-015-0299-7
or in the preliminary report with similar title and content which appears in RG under my name.
For SISO plant of any order, even 20 or 100, the Simple Adaptive Control (SAC) methodology actually manages to use just one adaptive gain at the minimum or, to get better results, may add a couple more adaptive gains from a very low-order model.