What is it, specifically? On Elite, does rare drops increase while common drops decrease? Or does simply the quantity of items dropped increase? Or maybe there's no difference at all?
Effect of difficulty on treasure block drops
The guild Lancer Knightz has data on mission payouts. They don't have much for the new difficulty levels yet, but it seems that crown payouts are 20% higher on Elite than on Advanced, and 20% lower on Normal than on Advanced.
I can't comment on whether difficulty improves drops of materials, equippable items, rarities, etc.
Edit: Let me add that there have been countless threads on whether difficulty level improves the drop rate of orbs of alchemy. In every thread, the answer was essentially "we don't know".
To me, difficulty only changes the amount of crowns and heat dropped, not the materials. I don't know about equipment that drops because I haven't seen any after the Pokeman update went live.
I've gotten two books during the Black Kat event while only playing on normal.
Seems it's certain crown and heat increases, it makes sense since these exist in different types of magnitude (i.e copper, silver and gold for crowns). I understand it's hard to verify for rare drops like orbs of alchemy, but has anyone noticed an increase in Fire Crystal drops?
@Sacrontine
I do notice a large increase of fire crystals on elite (or maybe just less vials and hearts in boxes :P)
There's an obvious difference. Drops both increase in quality and quantity.
The end level report proves it. Try to do a single level twice and see the results.