Add written bios or descriptions for wielders, towns, items and curios
One great aspect of Songs of Conquest is the fact each wielder in a faction has its own visual design (portrait, full-body portrait for the item window, animated model on the map) : it gives better clarity and personality to each hero, and often help easily guess what their strengths are.
That said, I feel like adding even more flavor to each hero, but also other elements of the game (items, towns or even curios) would make the world you have built even more expressive without having to play the campaigns to be aware of each element of the lore. This is something that the Heroes of Might & Magic series did quite well at least up until the fifth opus : each hero or town could have its window giving an idea in one or two paragraphs about their past, and below the title of items and curios, there was often a short description of its place in the world.
For Songs of Conquest, which uses different curios or items for similar effects, text would allow more uniqueness for each element.