We have a 57 plate 3.0d and it tows perfectly. The fan upgrade etc only really applies if your a towing something very heavy, over 2,000 kgs which is not many vans. Ours is 1300 and you could easily forget it's even there.
Also had no reliability issues. The issue with going off road is nothing to do with the car, it's the tyres. Most x5's have very wide road tyres on them which wouldn't work on any 4x4 off road. We also have a set of 19" with narrower winter tyres and it will drive through anything with these on.
Regarding the tyres, our Discovery 2 V8 has the 255/65R16 tyres as fitted to the X5 and Frontera, and we have had no issues with towing at all, roads or rough ground.
I don't change the tyres for winter either, and we have just completed a 2000 mile trip to Holland and France with the big 6-wheel trailer behind with no problems. Got home last night.