Very good topic @Suneedh Wrangler!
You will surely find different answers to your questions. These are mine:
After a desert drive, do you always go for a full wash, including underbody? Or do you only do a full wash occasionally and just rinse the important areas most of the time? i wash my cars at home and rarely go for full or underbody wash. I brush off / blow off the dirt and dust from inside the engine bay as i don't want to have any water in there.
Do you do anything special after drives (like checking skid plates, suspension, bushings, brake dust, etc.) or do you mostly just wash and go? after the drive i tend to listen if a new suspicious noise has come up
When it comes to fluids — do you change engine oil and filter earlier than the manufacturer’s recommended interval because of the heat, sand, and harder driving? I change my oil around 7000km (fully synthetic Castrol/ROWE/Mobil1). Air filter i clean myself regularly (10 days).
Same question for transmission oil/filter, differential oils, and transfer case oil — do you stick to the recommended schedule or do you shorten it for peace of mind? I stick to recommended schedule here as i don't push my cars that hard.
Do you use the agency for everything, or do you prefer trusted garages? (And if so, what’s the main reason — cost, quality, speed, or experience?) my cars are too old for agency, so i go for trusted garages.
And lastly — any “must-do” maintenance tips you’d recommend to someone who wants to keep their car healthy long-term while enjoying desert drives regularly? You've covered most of it here above, but i always recommend to check your engine and coolant levels before every drive, and keep a good watch on your temperature gauges (engine/transmission) throughout the drive. I also don't do any high level drives towards or in the summer to avoid overstressing.