I like how exchange feature was implemented for scrolls, because finally tons of low tier scrolls, I got for farming are finally usable. And more in-game mechanics use silver and gold tier scrolls than bronze.
But there are other resources where you would easily implement this feature.
One of most wanted resources that also should have exchange feature are titles. Many middle or late game players also have tons of bronze titles clogging their inventory after farming cards or events. You can also keep the exchange ratio as for scrolls (100 low tier titles for 1 higher one). And like scrolls, bronze tier titles are not as much used as silver and gold tier ones.
I know about books being mostly used for shorting the time of trading in the Dojo, but it could be useful to add exchange feature to them too (not as much wanted as for tittles). Because also, silver and gold tier ones are more used for developing your friends than bronze ones. The same exchange ratio as for scrolls would work there too.
Type of resource that you shouldn't add exchange feature, because it could break some other parts of the game and balance:
Personally, I would like to change all of my tons of bronze woods (from farming cards) into silver ones, but it would make one of the game's features less attractive. Main source of silver woods are Daily and Weekly Arena and main appeal of arenas are resources you could get from it. Adding exchange for woods would make most people less likely to do Arenas.