Suggestions for a SOD mod.

Ideas like the ones mentioned in the header won't appeal to players. There's the Rose Cavalier plugin for single-player, and multiplayer has its own features, such as the Guild of Mages overhaul. What else can be "improved," and, more importantly, for whom?

What does the Rose Cavalier plugin have to do with it? The goal of this plugin is not to change the gameplay. The Guild of Mages overhaul, in my opinion, is already too significant of a change.
I didn't understand your post – you yourself mentioned earlier what you would like to change in the game.
Regarding the ideas in the header – in my opinion, they are too radical. However, I agree with Kventin that opinions on this matter may vary. For me, "polishing" means one thing, and for him, it means another. For me, it's something like this: Mysticism on Expert +5 instead of +4, mana cost for the spells Hypnosis and Mines – 15 instead of 18. Several changes of this kind...
And, unfortunately, I completely disagree with the desirability of changes for most players – the suggestions from players that I read on the forums only cause confusion (in a mild way)...