Well, my 2 penny worth on some of the subjects discussed so far:
Discovery 3 as an expedition motor, no thanks. the words landrover and electronics don't sit well together and trying to sort an electronics gremlin that has immobilised you in the middle of the desert doesn't sound appealing. thats why I just bought a 300tdi defender.
TD5, mums got a disco one and it's the worst 4x4 I've ever driven. wouldn't have one if you gave it to me!
Trailers, I have never tried one on an expecition, but everything I have read about expeditions says don't do it! I have used them on miltary vehicles and would say they put massive shock loads through your chassis and drivetrain, ad considerably to the drag through sand and mud, are a bxxxx to reverse, especially off road (and I've spent several years driving artics so know how to reverse a trailer!) and they are not at all easy to recover if seperated from the vehicle. If you need a trailer you've got too much kit!
I have taken my H60 landcruiser to russia and Africa and it was fantastic, although the H60 I bought to travel with mine taking a load of school books to the Gambia needed repairs on a daily basis. although they were straightforward to do and nothing seized.
On the way back though my gearbox started to fail, I think as a result of (relatively) high speeds through europe in hot weather. I looked at 3 landcruisers for replacement boxes and they were all on their last legs, is this a weakspot?
Tom Shepperd, of vehicle based expeditions fame drives a merc G wagon now, and he's pretty much tried them all!
the only reason I now have a 130 is to turn it into a camper is cos the missus wants a toilet and I can't fit that in the landcruiser!!
'If you want to go on an expedition take a landrover, if you want to come back take a landcruiser!'