I'm thinking energy will refil outside the dungeon/map, and probably more to slow people down and get the story, than it will be to force purchases. Most people are conditioned to drilling through updates to cap and a week later, saying we need more!
I took my time in SL until voleria, i almost missed the L36 cap vanity on one toon, and thought maybe the L41 cap might come and go quickly but no. So i have spent the last 2+ months farming and selling items and its my own fault for rushing through it.
I may be wrong. I think energy was a control to get people to slow down and enjoy the story, instead of skip scenes and grind it out in a day or two.

One thing is for sure, we will know soon enough... and i can't wait to see it!