I'm keeping everything Williams did in. Anything I'm adding is intended to make the film feel more "complete" and not a rough workprint. It is a thin line, but I'm trying to be as faithful as I can.
The goal is to make the film easier to watch than the workprint, with cleaner picture quality, more finished material, more music.
Still, thin line.
It is necessary to add music in order to benefit from the clear sound and sound effects of the Princess and the Cobbler soundtrack. I knew I'd have to use some of the Princess soundtrack to cover places in the workprint where sound was missing (like about 20 minutes in the middle of every copy I've ever seen), and to use the clearer voice tracks for Price, Davies, etc.
This required me to add some music to cover the transitions to the Princess soundtrack.
I really have no choice in the matter, but I do feel that adding more music improves the unfinished film. It's clear enough that the film needs more music - some scenes go on for a long time in silence without it, and would always have had more music in the finished film.