I know, it takes great practice, and a huge time investment. I'm seeking guidance on the most efficient method to get to the point of recreation of ephemeral images in my mind.
I've probably got more experience in 3D modelling (comes more naturally thus far), but if it's easier to recreate life-like images in a 2d medium, then I'd probably jump that way to get up and running quickly.
What about first capturing the images in words? Write down the details of the images. This will give you an archive of inspiration.
Personally I would start in 2D first. I am experienced in 3D modeling but I always start in 2D.
When I look at the works by preeminent sci-fi artists, I'm blown away by the level of detail of their work. I'm sure that it takes them considerable time and effort to create those works. So either way, I'd think you will need to accept that you need to practice a great deal with your preferred methods and techniques.
I like sketching because what I want is an impression of a scene in my mind. My friends seem to want more of a replication, which I think takes too much time and never looks the same as my mind.
Repetition is the mother of skill. Pick something and practice daily, even 10 min.
If the end result is really important you can hire an artist. But you'd need some art skills/knowledge to art direct.
But just have fun, it's a long journey.
The most efficient method is to start trying and not stop.
Efficiency is a fool's game.
What matters is the end result.
And that's a matter of hard work.
The reward for good work is more work.
Good luck.