So I pondered deep delves for a while. With a little work, you could tweak the special treasure room and the treasure multipliers so deep delves are more rewarding than 2X a regular delve (which they currently aren’t). The problem is, deep delves are just regular delves with one room difference, and the new room isn’t all that exciting. People probably see all the gnomes they need thanks to GAP weekends, so why bother with a lot of work to see one extra? Especially since most gnome rewards aren’t worth the 10k gold cost for the deep delve.
So here’s my plan for how to make deep delves better:

Each faction gets a new delve map with 15 rooms, and the rooms range in difficulty from 3 to 8. Delves are all about multipliers, so the rewards would be good, and the difficulty 68 rooms would be unique to deep delves, making them different. Of course, someone would have to come up with some difficulty 68 rooms, but it’s been two (?) years since we’ve seen any new delve rooms, so there are plenty of nondelve troops to choose from.

One of the deep delve rooms would be the special treasure room, but it shouldn’t have a random gnome. Daemon gnomes would make sense here, except I’m guessing nobody really likes daemon gnomes. Maybe the deep delve treasure room could be more like the epic vault, with a daemon gnome, two treasure gnomes, and the hoard mimic. And then you could change the epic vault to NOT have a daemon gnome, and make everybody doubly happy.

Since the deep delve would be twice as long as a regular delve, the 2x sigil cost would make sense, and it could remain the same. The 10k gold cost seems pointless (just like the 1k gold cost for arena runs is pointless), so it would go away.
So you’d get a delve that’s different, more difficult, and more rewarding – none of which is true for the current deep delve.