...That is the question.
In my previous question, I asked about coilguns, how powerful we could make them and their plausibility. In that thread, and the discussion I had with Starfish Prime afterwards, I came to the conclusion that even the level of sci-fi technology I was aiming for, which is pretty small-scale compared to most other sci-fi settings, is beyond what we know can be accomplished.
That's not to say that we definitely can't create short-barreled coilguns with muzzle velocities in the dozens of kilometers per second, or fusion rockets with both high thrust and high efficiency, but we don't know for sure that they are even possible. It may be that there's an upper limit to technological progression, and that making starships that do what I want them to do just isn't possible, and therefore isn't realistic. If such an upper limit exists, it is all but certain that Star Trek is well beyond it.
With this in mind, is there really any point to going into great detail about how the universe works, and trying to make it as realistic as possible, when I know personally that it probably isn't possible? If I'm going to shrug my shoulders and go ahead and give my ships engines that I know would realistically melt within ten seconds, should I even bother to explain what those engines are and how they work? Or should I handwave and be nebulous?
I'm sort of leaning towards keeping the technology level theoretically possible, if you had absurdly ridiculous efficiency, but just keep it in the background without going into any detail about it. That way, if someone who likes poking at sci-fi realism - like me - comes along, they'll take a look at the numbers and go either 'that could work' or 'that's unrealistic' rather than 'that's completely absurd'.