OK - I'll take the bait. I wouldn't put the 120 in the same class as the RR sport - more in the Disco 3 or 4 league ito space etc. Both have a 3.0 tdi common rail motor - the disco is a twin turbo V6 though
I've had 2 x 80s and now the 120. The trick is to try to minimise what SWMBO thinks is necessary to take with on a long trip
Never easy. I mean - how many kitchen sinks do you really need??
The boot depth is fairly similar, but the 120 is a fair bit narrower (but taller) than the 80, so you end up with a strangely shaped, narrow but tall space to pack in. The side-opening door is also interesting, because it slopes inwards and so robs you of quite a bit of room ...
The 120 drives more comfortably than the 80 because of the IFS - but I always found that the live-axle 'Land Cruiser lurch' almost entirely disappeared once decent suspension went on - or maybe that was just me justifying it
17" rims are a pain, as is the rim off-set, and not being able to go to 16" due to the calipers doesn't help, so tyre choice is fairly limited and more expensive than it should be.
So - would I overland in my 120? Absolutely. Am I concerned about faulty ECUs? Not really. If I drowned the 120 I'd have a big problem. But if I didn't do anything absolutely stupidly extreme I think the electronics is a no-brainer. I've not seen anything on MUD, PradoPoint or Toyota 120 forums that points to a weakness in the electronics. I've heard of a 150 with a problem engaging the push-button low-range selector - but that was due to the cable being pulled off the switch underneath when they went trail-blazing, but some under-armour would sort that, which I'd have on any overlander anyway, 80 or 120.
What does give me cause for concern is stuff like wheel bearings and diffs, and on the autos the in-radiator gearbox cooler. Would that stop me? Nope - take a spare set of bearings if you're that worried, and make sure the maintenance is done properly. Again, I've not heard of the KZ-TE cooling failure on the D-4d. If the injector issue is sorted, then I think the motor is fairly solid - admittedly not in the same industrial-strength way as the 4.2 - but that wouldn't stop me either. Access to parts in remote areas is definitely one to watch, but becoming less of an issue now the UN is using the 120 more and more...
Main diff is internal space - the 120 has less of it. More creature-comforts though. Also more plasticky bits, like all modern cars. They're fairly close ito power and get-up-and-go. The 120 already has an inter-cooler and can be easily chipped for 200hp without (apparently) breaking anything ...
A well-set up 120 gives astonishingly good consumption too.
After-market accessories are readily available - Kaymar and ARB do a lot, and there is an after-market extra fuel tank now available, because we didn't get the twin tank system like in SA or Oz - pity - 190 litres of fuel on-board would be a boon. Knock-off bumpers etc. are also available. Roof-racks are easily done, and are a straight swap, I 'think' with the 100 for leg spacing. Snorkels are also easily available, as is after-market suspension, even for the LC5 with it's air-suspension (which I've grown to love for it's auto-levelling feature if nothing else - any load in the back and your ride-height is unaffected).
If you can fabricate stuff, you should be able to prep it to your heart's content.
Would I go with diff locks vs ATRAC? Think both at the back is a benefit - not sure about the front. The fact that Mr T has gone with both ATRAC and a locker at the back on the 150 and 200 makes me think I'm on the right track, so I'll be fitting my eLocker asap. ATRAC seems to need a bit of traction to engage properly, and I sometimes think we may not give enough wellie when we get, or think we will get, stuck. So far, touch wood, I've got through the tricky bits the same as the 100s or 80s bar two notable exceptions - once was because the centre diff was bust and didn't lock, the second time because I chickened out at the last minute, backed off the juice and ran out of momentum in a mud-hole - driver error (oh - and same when I got myself grounded on the belly when going too slow on a river entry ...)
Would I prefer an 80 to drive through Africa? I dunno - maybe. If I could have ONLY one, and it had to be a daily drive and a holiday vehicle and an overlander and a green laner etc. etc. - I still dunno.
Probably the 120! Depends on whether SWMBO is coming with for an extended time I guess
I have to re-design my packing system anyway, whatever I do. Or pack less
Best I can say is to try get an extended test drive in a 120 and see for yourself. It's horses for courses to a large degree. The 80 is less refined and possibly more robust, but they're all getting a lot older so things are breaking. The 120 is more refined, a bit 'softer' in some areas, but I reckon just as capable ... as an overlander. If you want extreme lifts etc. then the 120 is not the vehicle, not without doing masses of work on UCAs, ARBs, steering, diff, etc. And if you want to run 35" tyres you may need to re-gear diffs, etc. But that's not for overlanding, is it?
Just my tuppence, and HTH.
Cheers