I have very recently retired, therefore I am pondering at similar ideas.
For me is to understand, and I mean really understand, the analog functions. Understand not only how to fully calculate a particular function, but understand component sensitivity, how different non-ideal characteristics affect performance, the tradeoffs between dynamic range, distortion, noise, frequency response, power consumption, input impedance, etc, etc.
This is a a three pronged approach:
1-hand calculations, well with Excel’s or Mathcad’s help.
2- Simulations
3- Actually building the circuit and probe around with a scope.
Thus, not a complete project per se, but to master my “analog toolbox” to be ready when the need arises.