50mm Madness!!

[I @ M]

(and yes I am seeking professional help for my NAS).

Why bother? save the medical bills and put the money towards a[nother] good lens. The end result is the same, you end up poorer and happier.

Now the questions. Is the only difference between the D & G models the focus motor?

No. There are quite a few things different, some important, some not so important.
The newer G lenses have all the latest fancy coatings on the glass.
They don't have aperture rings.
They have a different build quality.
They are bigger and heavier than the older lenses.
Plus a few more ---

Is it really worth the extra money for the 1.4 over the 1.8 considering both my bodies are very good at high ISO?

Yes because if you really want to photograph at F/1.4 you can't do it with an F/1.8 lens.

OK, you have the 35 F/1.8 and that is a great little lens so you already know what the field of view is like on your 3 other DX bodies. That is going to be just about exactly as you will see with a 50mm on the FX body. If that focal length suits I would be inclined to save my dollars and buy ( if you have to ) the 50 1.8 G.