FWIW, I have an 04 Disco, and I often think that if I had to start all over, I'd get an H3. With the Adventure package, you get 33" wheels and lockers from the factory. I've heard you can fit 35's without doing much to them. Both engines available in the H3 (I5 and V8) are modern designs that should blow away the Rover V8 in terms of reliability and economy. The Rover V8 is certainly the worst engine I've seen offered in a modern car. I'm guessing the trails around your area (even the "easy ones") are similar to here, meaning lots of deep mud. 35" tires would really help, and it's fairly difficult to get them on a Rover.
By law, the H2 and H3 will have to be supported with replacement parts by the OEM for 14 years from the date of manufacture. Not to mention, they did sell a number of them, and I don't expect we'll really have a deficit of available parts. While a Hummer is no F-150 (in terms of numbers sold), surely nobody is going to suggest that a Land Rover has better parts availability in NA. For example, LR sold about 200,000 Range Rover Classics throughout the world, much less in NA. Hummer sold about 150,000 H3's, mostly in the US. The Range Rover hasn't been sold for 15 years, but is anybody claiming problems with parts availability?
Furthermore... have a look around various online Rover communities, and see if you like the crowd. The US Rover online community is fairly unique. I'll leave it at that.