[Concrete]

ShadeTree,
you are doing great and your wife is on board too

you are right on with a lot of what you are doing
but a couple of comments

Originally Posted by ShadeTreeMech

While a mpg meter would be nice, I've had one before, and I know get into top gear and staying there is the key, as well as gentle application of the throttle and keeping the revs as low as possible nets the best fuel economy. And letting the van coast in neutral on the downhills brings up economy. I know this because I idle @800 rpms while I coast at much higher rpms.

this might not be true
even with lower RPMs - the in gear config could be running on virtually no gas
because the wheels are turning your engine for free
depends on how your vehicle is set up - I do real well In gear
need some instrumentation to know for sure

Besides I'm scared of accidentally "missing" neutral and dropping it in Reverse or Park at highway speeds
one mistake like that would burn a bunch of gas money

I think part of the reason I'm pressing on the aero issue is that the average speed limit for this van's regular route is around 50 mph. That may not be 70, but that is a consistent amount of higher speed

I like the aero stuff too but...
50 mph is not prime aero territory because drag is a velocity squared thing
it is not 30% more at 70 than 50 it is actually doubles from 50 to 70
so you can basjoos the van config or... just not drive 70

That and some of the factory plastic "belly pan" under the radiator has since been misplaced on the highway somewhere, leaving a flat brick right in the way for the wind to hit. So I suppose I'm wanting to restore the original aerodynamics and maybe improve upon it a bit.

Whoa! - new data
you are not at factory .35 Cd - you are more brickish
how big is your "brick" and what cavities opened up with this damage?
belly pan may be worth while if you have a barn door open

I know the earliest version of the villager had a partially blocked grille, because it had a light bar in place of the wide open grille I have now. As much as finding that older version of the grille is desireable for maintaining a stock look, a mod of my current grille is likely to be cheaper.

Grill blocks are a double bonus
aero and higher engine temps quicker
depending on your van and it's set up this could also be significant
my milage is pretty bad until the engine is warm
grill blocks are so amazing, I wonder why they have such honking big grills at all
but don't over do it - cooked engines are not efficient

I like basjoos's philosophy: I won't do it unless I can earn the money back fairly soon in gas savings.

Amen

BTW
go for the new plugs and wires - good maintenance and good for FE