First off, I love the recent Underspire changes. I’ve cleared it weekly since it was released, but the additions of more room types have definitely made it more fun and made me want to do more than just clear Diamantina every week.
That said, I feel like merchants are now underused. I use trinkets each week on the final 2 bosses but otherwise don’t use them. This previously meant buying them from merchants because I didn’t get enough from guardians to cover my usage. However now that we have treasures and traps and trinket rooms I have more than I need, and the merchant offers go unused (I also never buy the keystones).
The merchants can still sell the keystones, but I’d love to see their trinket offers replaced or expanded by something else. They could provide single purchase options comparable to what a travelling merchant sells (imperial deeds, writs, dragonite, pet food, etc), and it’d be worth checking to see what they have for sale instead of skipping them entirely (which is what I currently do).