This is an idea for people who don't or can't play every day.
The concept:
Add a new item to the game called the "Mist Capacitor." It is used to refill the Mist Tank, and cannot be used directly for any other purpose (like crafting). You still make purchases using CE and Mist Tank energy ONLY. The Mist Capacitor only stores extra energy so you can refill your Mist Tank after it is depleted.
The Mist Capacitor accumulates energy only while the Mist Tank is completely filled, and it generates energy more slowly, too. Like the Mist Tank, the Mist Capacitor also has a maximum energy storage so you still have to remain active to get its benefit. The key here is that it's still better to use energy from your Mist Tank when possible. A perfect player who wants to maximize their Mist Energy would never use the Capacitor. It is just a benefit for the rest of us who are not perfect.
It could even be a minor crown sink by letting players "upgrade" their capacitors for a cost. The upgrade would not help it regenerate any faster, it would just let the capacitor store more energy before it maxed out. That is, it would let you leave the game alone more days at a time.
So that's the general idea, now I'll drill down to the implementation details, which of course could be modified as long as the spirit of the above intent is maintained.
The technicals:
-All players are given a new 0 star item called "Mist Tank" under the Consumable tab. It has no effect until it is upgraded. This represents the 100 energy Mist Tank you already have in the game (it kind of bothers me how it's presence is not indicated in your inventory so I put it there!)
-A vendor sells tickets to upgrade the "Mist Tank" into the "Mist Capacitor" (it's still also the "Mist Tank", but the Tank is unchanged by upgrading so the name reflects this). Each ticket adds one star to the item and increases the Energy capacity of the Mist Capacitor by 50, starting from 0 capacity at 0 stars. When it becomes a 1 star item it is renamed as the Mist Capacitor.
-Tickets cost 5000 crowns each (TBD)
-The Mist Capacitor can be used from the inventory whenever it has Energy. Using it fills up your Mist Tank as much as it can, but not higher than the 100 Mist Energy limit (again, the Mist Tank as it exists currently in the game is never changed by this suggestion)
-Mist Capacitor regenerates energy at 50% the rate of the Mist Tank (ie. One day refills only 50 energy in the Capacitor), and it only regenerates while the Mist Tank is completely full, so just one of the two is regenerating Mist at a time.
-Energy cannot be spent from the Mist Capacitor for any purpose other than refilling the Mist Tank. Therefore this cannot be used as an exploit to make crafting or other CE sinks cheaper.
-A maxed Mist Capacitor is a 5* item which costs 5 tickets (ie. 25000 crowns), stores 250 Energy, and takes 5 days to charge. This is the perfect size for someone who plays only on weekends.
-No one is forced to ever buy any tickets or in any way interact with the Mist Capacitor if they choose not to, and it will not effect their game at all by doing so.
What say ye?
Not bad actually