Endless mode is proving to be pretty fun. I believe I've unlocked most of the optional content from the main game, and will, upon clearing the fourth dungeon, finally get to the post-game content. The biggest barrier to forward progress I'm facing lies in getting my adventurers to actually buy appropriate equipment. I'll see them in the shop fairly regularly, and yet, half the time, when they pick an item off the shelves, it will either be something they can't use or inferior to their current gear. It's especially problematic because you can only buy limited amounts of the best stuff, so putting top-tier equipment on the shelves just winds up empowering random NPCs (seriously, little girl, what do you need with a demon-slayer sword?).
There is a lot of grinding potential in this game, and if you want to max-out all the adventurers, explore all the dungeons, and unlock all the fusion recipes, you will have plenty to keep you occupied for a long, long time. I'll confess to finding it a bit tempting, myself. Recettear is simple, but diverting, and its low difficulty and steady pacing would make it an ideal game to play casually.
With only four hours left, I'm not sure trying for 100% completion is necessarily a great use of my time, however. My next goal will be to finish the Obsidian Tower and give Survival mode a try.