Current QM models say it will be impossible to access the parallel Everett
universes, but if non-linearities are ever introduced it might become
theoretically possible. I don't know about the energy part, but it would
certainly be of tremendous philosophical impact to learn that parallel
worlds are real, and perhaps even to be able to communicate with them.
You could conceivably talk to dead relatives, you could see how your
life might have been different if you had taken other choices, you could
get the effects of quantum computing, access works of art by people who
never succeeded in this universe. It would truly turn things upside down.
(Larry Niven had a story in which such a discovery led to nihilism and
depression, but I think the consequences would be more complex.)
Hal