Excellent points... yeah I was thinking about this this morning when I was preparing to make the New Years sale purchase... I obviously only want to do this once and want to go into a ~$1000 investment knowing that it will handle some changes in the future. In order to get the sale price, it looks like I'm stuck with the 21 spline input. This is a pain in the ass.
I have run Moab 3 times with a single 4.70 case with 4.88 gears and 33 inch tires. This was with a stock 22R and standard transmission. There were times that having lower gears would have helped, but I have not been stopped anywhere for a lack of lower gears. I am going dual ultimate in the 4Runner more for the middle set of gears than the low-low option. If you get the stock geared crawl box you will have adequate gearing for everything but the extreme rockcrawling.
The owner of the local 4x4 shop that I do business with actually runs 3.8 gears in his Jeep rather than the 4.3 because the 4.3 gears are too low for hillclimbs in the mud (Washington State).
If your budget is set I would get the stock crawl box (MC-14401), or upgrade to a complete dual ultimate 21 or 23 spline. Sometimes spending more or saving longer is worth the investment long term. I would put the twin stick money towards the cases as I have not found as much utility with mine as I expected.
Power and driveability. The 22rE sucks...
I have seen a 4Runner on 37 inch tires run 80 mph with a mostly stock 22RE. My stock 22R will run 70 mph most of the time without problem. Durability and Reliability are also things to consider. If you are going the HP route rather than gearing, then you don't need a 4.70 gearset.
