For your application, I'd do the following first:
1) Sell the new MTs while they're unused or exchange them for ATs - better grip on road and off road too (except in mud, wet grass or for extreme rock crawling), better wear, better fuel consumption, less noise...
2) Uprate the suspension with HD rear springs and OME or DeCarbon gas dampers. If you have air suspension, get a conversion kit ASAP - it's a liability on exped vehicles.
3) Aircon - if you don't have it, and an ES should, then in the desert it'll be beneficial, saving you from having the windows open in dusty convoys.
4) Fuel capacity - long range or additional tanks are more convenient, safer and less easily stolen than cans, though a single can is useful if you do run out and can get a lift to a service station. I agree with Terri-Ann that the roof rack is no place for fuel (it's illegal in Italy and Switzerland, and no doubt many other European countries, but should be illegal everywhere).
5) Battery - running camping equipment will drain a battery, and while a bigger battery will help, the redundancy of having two ordinary batteries is better than one super-duper battery.
6) Comms - inter-vehicle comms are very useful, but if you're travelling alone, reliable long-range comms are essential. HF radio or a satphone would be perfect when out of range of phone and VHF systems.
7) Storage - safe stowage of bulky gear is essential for safety in an accident and to prevent load shifts when at high body angles, but a proper system will also make accessing kit easier and quicker. Interior storage is preferable for CoG, aerodynamic efficiency and also security reasons, but if you need a roof rack, I still rate steel racks over aluminium - they seem to crack less and the ali racks tend not to have side rails to help retain the load. Boarding a steel rack is a good idea as they tend to have open frames, but remember that the weight quickly adds up.
8) Recovery - a slow but powerful winch is nice but rarely required. An 8274 or similar is overkill. You just need strong recovery points like a NATO hitch at the back and towing pintles at the front. They need to be accessible when bogged in, so JATE rings are not good. Strops, ropes, shackles (a ground anchor if alone) and a farm jack are all you need.
9) Spare tyres - one is essential, but a second could be very useful when travelling alone. Tricky to mount on a Discovery unless you have a roof rack, and they're quite heavy to be up so high. Tubed tryes and trye and tube repair kits might be better, but you meed tyre irons for that too...
10) Vehicle protection - stronger steering rods, diff pan guards and a fuel tank guard are worthwhile. Less so the fancy bumpers, though they will give you jacking points and somewhere to mount the front recovery eyes or pintles. A conventional mushroom topped snorkel (not the forward scooping type like Safari) will help prevent dust clogging the air filter in dusty convoys but is not essential. Paper filters are easily tapped out to give them basic cleaning, while cotton performance filters would be a bad idea.
11) Water - a big flat tank in the rear foot well should keep the CoG and any sloshing under control.
Ultimately, though, work out what you need, not what others need for their application or what looks impressive. It's usually the simple, cheap and mundane things that are most beneficial.