Feature idea helping fix spell (and other common resource acquisition)

With the introduction of the new spell system there is a huge disconnect between higher level players and their spells.

I for instance have a good number of legendary and mythic scrolls but having no need (prior to the update) and have since travelled beyond the normal means of acquiring them, I have no or very few uncommon and epic scrolls. This leaves me with hundreds of spells at 1 or 2 stars and makes it difficult even for me to level the spells I use commonly.
It also makes experimentation difficult as it means spending rare resources (obtusely the most common of scrolls and runes).

Suggestion - New feature called “The depths”

This is basically an endless dungeon “Tower of Babylon” style challenge.
Each level is populated by a (random?) monster starting from level 10
Beating the beast results in immediate drops (no chests) and unlocks the next level.
Every 10 levels you fight a boss and it’s henchmen (Dungeon style)
Upon beating the boss you unlock that point as a starting point for future runs. So if you reach level 40 but fail to beat the beast at lvl 43 you can restart the depths at level 40 in future runs.
As you progress rewards for each fight improve.

Access to the depths is gated, players will receive a single depths key once a day.
Additional passes can be sold in the store, found in challenges or provided as subs incentives. Price point suggested at 5x the value of diamond keys.
Using a depths key by default start you at your deepest level as described above, but also allows the player to start at level 1 (allowing them to acquire lower level resources)

Depths passes will also be available, these allow a player to automatically play through the previously unlocked levels to their capped point acquiring all of the drops from defeated foes and then allowing them to continue their exploration.
Depth passes are obviously valuable commodities and should be valued at 10* that do dungeon passes.
These can also be sold in shops for gems or crowns as well as given away as valued subs items or rare drops. Perhaps there can be a crafting chance at legendary or mythic follower level giving a good reason to level them up.

Supporting the feature with weekly or monthly leaderboards based on highest level of progression with depths passes and keys for the deepest divers provides additional incentive for regular participation.

Additional opportunities include enabling parties, timed runs and many other things not mentioned here.