I really liked the Nightmare difficulty this year.
Yes, it was harder than in past years. And yes, the Coaches (in as much as I noticed) warned us of that fact when we asked for Nightmare.
I don't know if it's safe to make the assumption that all Nightmare parties will be equipped with Legendaries and Artifacts. Fully min/maxed with URs? Yes. But if you set Nightmare at a level where Legendary equipment is necessary to make it through, then you're setting the barrier too high for people who just don't have that $$ to invest. Make it UR+, and if people kitted in Legendaries & Artifacts want it tougher, they can do a 5-man run, or choose to go in with no healing potions, or slide with their off hand for a challenge.
The Treasure Stamps thing, tho....
I've been thinking about it quite a lot, and I think (in retrospect) that I like the new ruling.
I like it for the Hardcore & Nightmare groups, at least.
Please, let's go back to the old ruling for Normal mode ("Did you solve the room? Then you get the treasure!") so New Players are not adversely affected. If a new player gets to use their awesome Boots of Lava Walking, more power to them! If newbies want to brute force it.. they take damage, and have to spend valuable resources healing up. Let them make that choice.
Let Hardcore have X chances for mistakes (1? 2? maybe 3?)
Then... give Nightmare zero tolerance.
I mean, let's face it: If you're playing on Nightmare, you've got some URs, and odds are pretty good that some of those URs will be treasure enhancers. You're not going to walk away with Zero Treasure, the way newbie groups might.
But whatever you do, make sure the information is communicated ahead of time.