I'm told the most mathematically efficient way is to do what you described but leave three blocks between each branch tunnel. Since most veins are 2x2 you'll never miss any by leaving 3 blocks in between.
I suppose, but I think the completist in me would get annoyed at the hidden row.![]()
Ah, but there is no "hidden row." Think about it.
If most veins are 2x2, then having two parallel horizontal shafts with 3 blocks in between is guaranteed to expose the vein in at least one of the shafts.
Oh yeah, I realize this, but it would still come off visually as one row being hidden. That would bother me.

And that's an impressive looking mineshaft, btw. I tend to dig down on a 45 degree angle, myself. Makes it a bit more work to get back to the surface, but I find it makes the digging process more flexible—I can avoid caves and lava pools if I want\need to.