I've always thought that it would be better if the Mill Spares button was changed to a Show Spares button, i.e. acting just like any other filter button in the collection manager. That would then give you a view of all the cards you owned that had extra copies that could be milled as spares.
The case where Standard plus Premium copies gives effective spares could be incorporated here too with an include / exclude option.
Once you were at the view of all your cards that had spares, you could utilize the other existing filters to narrow down the cards shown and then either hit a button to mill all shown (just the extra copies), or manually mill just the individual cards you wanted to. The number of scraps & powder to be gained could be shown here with the confirmation button as per current behaviour when you press Mill Spares.
Whilst they are doing this, I would also like them to expand on the filters and sorting in the collection manager. They could add a Rarity filter as a start. It would also be nice to have sorting by extra criteria than just Provision Cost, e.g. by Base Power, by Rarity, Alphabetically. Both ascending and descending. Preferably with multiple levels of sorting. If multiple levels of sorting is deemed too much work to implement, then default to selected sort option plus alphabetically.
I'd also like them to go back to showing the actual number of copies owned, not "9+" if we have 10 or more copies. Why hide information?
A lot of these facilities would have been more useful when full mill for changed cards was still a thing and people held onto their spares, but there's no reason not to have them anyway. If full mill for changed cards becomes a thing again, it would also be nice to have a filter button to show just those cards when appropriate.
