It appears the energy bonus for Carnivore is substantial, +50%. On completely empty tanks and Hard, a Carnivore cost $1500 to refill, and a Herbivore cost $1000. Firing a minimal blast of the mini-laser is $5, so it's probably 300 energy vs. 200.
The health bonus is +50% as well, not +25%. The Herbivore's ship has 300 HP vs. the Carnivore's 451 HP. I'm not sure where the 1 came from.
The 1 is probably a rounding issue. And yes, I discovered during the slug challenge that it's +50%. I've never finished Creature with anything other than red, cuz, you know, KILL, and even as the SLUG, I still got blue despite starting from green.
That said, if you're conducting a battle correctly, energy isn't critical. Oh, sure, in my first game I was constantly running out of energy when trying to fight, but I sucked. I didn't hire mercs to occupy the enemy ships, and trying to take on a T2 or T3's defense fleet by yourself will run your tanks dry pretty quickly.
Running out of energy during battles is not really the issue, as if you're invading a T2 or T3, you basically go in low and fast and just BOMB. It's rather Netrekky in that regard, don't hang around trying to dogfight, go for your objectives. Still, nothing more irritating than running out of gas in the middle of a terraform. That said, 50% more energy is not as impressive as 50% more weapon damage.
Once Energy Mega Packs become available, this bonus loses most of its importance, but it's still not shabby.
Energy mega packs obviously give you more energy to mega, so this hardly makes it less important! Rather, it makes energy mega packs better!