You are correct, we don't have to worry about corrosion or harsh winters. On the other hand further North the summer temperatures are much cooler. Our Texas summers are in the 90s in June and the rest of the summer temperatures are often over 100. And Summer temperatures last longer. The forecast is 90 for the next week. The comparison may not equal out but Texas has extremes as well.

Does it cool off quiet a bit at night? I vaguely remember from my brief time in Houston that during the day it was damn hot, and at night it got pretty chilly. If so, I think temperature cycles like that can fatigue plastics and rubbers cant it?

Yes, cycles will accelerate failure. I don't recall a chilly summer night. My guess the summer high/low varies 20-25 degrees and in the winter 25-30.

It certainly seems the E53 design/materals perform better in hot climates.

I've towed a 6k lb trailer and seen the OBC outside temp showing over 120 deg F, stop and go hwy construction traffic, with the AC on max. The X performs flawless in those conditions.

But when engine parts goes from 0F from sitting all night in the Polar Vortex to 200F operating temp in the winter you can bet that this type of extreme temp is more damaging to the material. Most Intermediate lever problems are experience by owners that lives in the colder climates such as the Northern part of the states or Canada.

I don't disagree. I don't keep track of what problems owners are having, mileage or the climate. Having lived in michigan many years I think you are correct. I didn't keep a driver longer than than 3 years to avoid the corrosion damage and worrying if it was going to start in severe winter weather.

I have an issue with the "intermediate levers" diagnosis - I had severe oil consumption & the smoke of shame issue at the same time. All techs said it's intermediate lever issue. However, I went with AGA, and changed the valve stem seals - and it looked like these were the culprit. After changing those, the issues are gone. Maybe the valve stem seals go kaboom quicker with those ambient temps differential. AFAIK, for the indy's & dealers it's quicker to give intermediate lever failure diagnostic (and more profitable - everything comes off anyways, and you can charge more for stuff they do with an open engine)- the heads have to come off, then they will change the valve stem seals & VCG anyways (hopefully with all the other seals) which are the main culprit of the issue.
The problem is, according to TIS, once the head is off, and you start changing the intermediate levers, how competent are they in replacing the other elements (rocker arms for example). The rocker arms (as well as the intermediate levers) have a p/n, a cylinder position AND a tolerance (stamped on each part) which will give the correct p/n (it's not a generic p/n like any other BMW part). If one of those has the wrong tolerance, the valve(s) will NOT open/close correctly. Then, you have the timing issue.

0.02