Great opening post! I, too, think about these issues as we go solo deep into the desert and we are not slow anymore
To me, it all starts from mild mods. Any bigger mods will result in extra wear and sometimes excess and fast wear. When I finally get 8112s with adjusters in the front (not yet in production), I may go just a tad higher in the front but will still stay under 2", certainly not over 2".
Then reliability of aftermarket components. You never really know when a monotube will give up the ghost. Sometimes, top end shocks can let go for no apparent reason. But it is a rare occurrence so I am not overthinking that. If having less capable shocks, carrying a rear spare is a good idea, for example using anything less than a 2.5 at speeds higher than what a stock setup allows.
For spares, I only carry tie rod at present. I whiffed on a good price for CV and rear driveshaft in January because I did not want to pay 100$ shipping. Now I wish I could have those prices. So I still carry no CV and no rear driveshaft. My concern with those is in crawling which we don't do much of but I would like to get those parts eventually.
I am all for preemptive maintenance but thankfully it is early for me. Changing fluids on all diffs/transfer case/lubricating the driveshaft, I do all that regularly. You can find a spare alternator cheaply from a junk yard but I agree on preemptive replacement at higher mileage. If you ever do water/deep mud, it is great to carry a spare anyway. At your mileage, I would probably want to have a new starter as well.
You have the sibling tires of mine. I love the ATZ P3. I got a nail in one of mine this summer trip. It stayed there for like 600 miles till I returned home and the tire finally could no longer stay above 20 psi. It was repaired by Discount Tire. But I bought a capable spare in result of this; I used to have a P-metric Wildpeak spare.
But yeah I really don't have much to say other than that I see things pretty much the way you do