Your comment made me think about how to improve a synthesizer design. Even with a modular synthesizer, where in the natural state every component is tweakable,

Your comment made me think about how to improve a synthesizer design. Even with a modular synthesizer, where in the natural state every component is tweakable, but has no effect (before you make any connections), there could be a way to provide feedback: e.g. have a light bulb whose intensity is somehow proportional to the effect the module has on the main out. Or have lighted cables that would allow to trace the signal from oscillators to the output (e.g. with a lighted dot that runs the length of the path).