@encryptedmind. Wow, I had not seen this topic until now. The tool that I have been doing since this summer goes right on this topic, but for powering the mouse and MIDI Input:
The main window (the one with the vertical sliders) just serves for that, manipulate the values quickly, even offering a visual screen that clarifies "where is each value" within its range. However this tool has not stopped fattening with other ideas, adding other windows for chords and manipulating effects parameters with custom controls for each effect. I'm still finishing some things. The use of the sliders is very simple. If you want to change or add a specific parameter, just drag the bar up or down.
Imagine what you can do with such a tool, knowing that the tool coordinates with the pattern editor. It may inspire you to learn LUA and make your own tools. In the end, "the trick" for a tool to be really useful and pleasant to manage always has to have a good GUI, and right here is where I'm constantly fighting.
I will unveil the history of this tool a little... A few months ago a veteran and well-known user of the forum complained that in Renoise it is difficult to control the delay parameter for each note and that it resolves complicated compared to a piano roll (understand what you have in front of you). You know, the fact of entering the delay parameter in the column, which visually does not show "where is". So I thought there must be a simple way to be able to visually represent where that delay is within the line/row, and that became a huge vertical slider for delay. In the beginning this was going to be my tool. But then I saw that it could be expanded for all other parameters and one thing led to the other, In the end it has become a tool capable of quickly bombarding parameters in editing tasks, both individual parameters or even in groups. A tool can be born that way. A simple idea that is expanding and becoming something much more complex.
I will continue to encourage you with learning LUA + API. I'm also curious about your project about your book. I hope in the end you finish it. It would be nice to be available in PDF format.