The holiday event deal is a pretty cool idea. You get both CE and a two week elevator pass. That's awesome!
So here's a thought. Once the event is over, why not apply that idea to all energy purchases?

Pretend for a moment that the holiday deal doesn't exist. You want to spend real money on the game. Let's say $6.00.
Okay so you have two options at the moment; either buy "subscription" or get energy for crafting.
If you buy subscription only you'll have to earn all your energy through trading crowns, but you can earn as many crowns as you like in a day. This deflates the value of crowns and increases the demand for CE.
If you buy just CE, you get to craft a few items but only get a few clockwork runs per day. Well that sucks, what if I want to play some solo and then play with friends later in the day? It starts costing CE which I don't want to waste.

So here's the idea: tie CE and elevator passes together and have them scale accordingly:

750ce = 7 day elevator pass
1600ce = 15 day elevator pass
3500ce = 31 day elevator pass
etc.