Given the low number of kms you will do in the vehicle, I think you'll find that the Disco will just age and depreciate. I agree with Phoenix that the Defender will hold it's value a lot better - having just bought a low km Defender myself (won't be low km for long though).
Walker makes a good point about considering a Rangie. I get lynched every time I say it - but a Disco is just a plastic Range Rover. I'm sure glad I've got a 1988 Range Rover and not a 1994 Discovery - though you may have to get an older Rangie, it's certainly worth considering (unless you're definitely getting a diesel).
The Defender also brings more character into the equation, and it's nice to have a "tractor" as a 2nd car. As far as comfort goes - I don't understand what people don't like about the Defender, 10 hours a day, 14 days straight of driving highway / corrugations / desert dunes and not a hint of a sore back. It may not be as plush when you sit in, but the Defenders seating supports you well.

