Thanks, BagginsBill. I have that CoE expression in pretty much any shader solution replacing a shader with both diffuse and specular. Since I do move the connections from those top channels down to Alt _Diffuse and _Spec, I was hoping for a decent idea of how to go about assigning diffuse and specular values, since the usual DV = 1, SV = 1 I'd be replacing wasn't going to be much of a guide.

Just trying to do maths: what exactly sort of value would Blinn(1, .4, .65, .4) yield? IOW, which channel of Blinn would be yielding the value that:

.*7 * (1 - setSpec))
**
would be evaluating? Looking at channels, it's not like we're comparing apples with apples... both have a color channel as the first one, but whilst diffuse has value, what Blinn yields must be some sort of composite of the rest of the channels. According to your node reference, Blinn yields a colour, and since:

"You can mix Colors and numbers in your arithmetic. Whenever you use a Color and a number, Matmatic first promotes the number to a Color (using the one-number rule)"*

what does happen in that expression? Or is it so complex a calculation involving far more than I could ever get my head around that I would simply be best off just accepting that:
.7 * (1 - setSpec)
is a good default Diffuse_Value to set for Diffuse, and to use the Blinn values as outlined above for most specular-type node replacements.

Just to show my line of... um... thinking... lets say that I'm using a Blinn node where:
Blinn.Specular_Color == WHITE (as in: Color(1, 1, 1))
...does it follow that setSpec == 1?
..in which case,
.7 * (1 - 1)
... no, that can't be right. That would have a value of 0. So, Blinn must yield some other number made up of maths done internally. As would Phong or Glossy or any of the other specular nodes.
I'm probably nowhere near understanding this, as this line of thinking must suggest. And I really am trying to break down questions into single units, although I don't do real well at that.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks