Here's the thing, though: It will take a long time to get right. And what, exactly, will we get out of it? I don't think we will get anything that can't be done faster and with more Boom TM than "regular" methods, such as thermonuclear weapons and fusion reactors.
Also, fission---fusion---bombs is a pretty nice way to get the "AW CRAP" emergency button we may need if they get lucky. That or we just go straight to pre-battle bombardment with excesses of thermonuclear weapons and win every battle ever really fast.
Okay, here's the thing. Science Fiction, at it's core, is about implication. There's hard Sci-Fi, which is about saying: "Okay, what are the implications for all our present technologies if advanced X years into the future?". There's space magic Sci-Fi, which is basically fantasy reskinned and where pretty much everything can happen with about as much justification as the invasion of Crimea, and as such it asks "What are the implications if magic were in space and used to do space stuff?" and that pretty much gives you Warhammer 40k.
Then there's soft Sci-Fi, which is where we are. Here the question is a bit more nuanced, because you're allowed to lie a little. You're allowed to invoke suspension of disbelief to get a few things through, but you have to play those things straight. This one is "If we we assume that X, Y, and Z are true, what are the implications of that?"
Bio-etheric energy isn't about saying that we have magic cold-fusion space goop, it's about saying "Okay, Many Worlds (MW) and Universal Wave Function (UWF) are valid interpretations of Quantum mechanics. Given that, here's how we can extract energy from it." Or, to put it in the framework of the above, "If we assume that MW and UWF are true, then what are the implications of that?"
This first move is an energy source. After that, you've only got to do your homework and think "Huh, okay, IF this was true, what could I do with it?"
Who says the enemy is going to "play fair". The nuclear option is nice, but not all that effective in space. It's powerful and can cripple ships with EMP, but the blast is much reduced. So it's not really an end-all-be-all, but fusion power is very easy to get, relative to exploitation of quantum mechanics. Fission is even easier. Developing these two simplistic power sources is easy.
The problem with "vacuum energy" is not its limits but rather the rate at which you can conceivably draw it. Fusion, however, paves the way to creating matter/antimatter annihilation. But first we'd need advanced magnetic containment....which is also very useful as part of a forcefield using plasma to melt and then absorb (Into the shield itself, ironically enough) incoming projectiles.
Typically, when you put something quotes, it means you're quoting it. No one said anything about playing fair, they talked about playing boring.
Also, vacuum energy is a terrible, terrible idea. If Chiefwaffles played it straight we could easily face a point where our reactors literally caused the laws of physics as we know them to go bonkers around our reactors. Let's not do that.
I agree, Fusion gives us a path to shields. AM reactors will probably be a thing, and I do like the idea of golf-ball sized fusion warheads, but... I don't think the game is going to go that way. It's not much of a game when your blast sizes start reaching the gigaton levels, you just blow everything up rather than allow capture.