All spot on stuff, as usual from you man. One issue with doing the spacer thing, which you sort of alluded to above, is that you still have to open the lid to check it. So every time, you're losing heat, which is not good for cooking or for efficiency.
The way I've seen to adjust the height on the conversion kits like a DoJoe is to raise it by hand with the peel for a couple mins at the end to cook the toppings better, which does sound like a beating. But I've also seen people having to do that with stand-alone ovens like the Ooni. Don't quote me on this, but I think @Anastasis has had to do some of this (maybe he'll weigh in and set me straight).
So, I'm not really seeing that much of a difference between an egg conversion kit like the DoJoe) and a stand alone oven like the Ooni). I'm sure you're right on the efficiency thing, but there's also the factor of having yet another stand-alone contraption in my yard to have to fuck with (DoeJoe being an accessory and Ooni being a stand-alone contraption). By the time I get done listening to all the surly experts, my back yard is going to look like a damn Home Depot parking lot...grill, smoker, griddle, pizza oven.