I had a Pathy for 3 years before replacing it with a D4. The Pathy was only a std 4 rather than the 550 however.
The Pathy is generally a capable vehicle. I had mine kitted out which proved a problem with towball weights once the Expanda came along. It was either remove the bull bar or leave one kid at home to be legal (do a search on here - I had a good whinge

) I also found the transmission was always hunting for the right gear when towing which became a real pain, and very fuel inefficient.
When changing over, I took the 550 for a spin and was impressed at the responsiveness (unloaded, and not towing), but everything else was the same as the Ti.
Taking a D4 out though was chalk and cheese. The level of refinement was miles beyond Nissans plastic and poorly fitting trims. The rear row seats I could sit in comfortably, rather than Nissans where my knees were either side of the middle row's passenger's ears. And the engine gave so much more than the 550.
Much hype about LRs higher costs for repairs etc, but I haven't found that myself. The servicing costs are annual rather than 6 monthly, and so far have worked out a little less than Nissans (overall). (if you can get a corporate plan as a company car they're free) Replacement parts aren't too bad if you shop around - LR will charge more than independants, or even less if buying from England, including shipping. The range of aftermarket parts is less than LC/Patrol, but I found that with the Pathy also.
The only real hassle is the 19" wheels. When I bought the Pathy, it had 17" and the tyre choice was near non-existent. I have found the same with the 19s this time round (There are only 3-4 types of ATs and no MTs in Aust). As for after market wheels - forget it.....
Due to the brake caliper size (which stop the car exceptionally well) the only 18s rims available are imports at $500 each, and then you still only save a few dollars on tyres, but a better choice. (The older TD model allows 17" though)
Where I saved though was not needing a suspension upgrade and/or airbags - with the factory adjustable suspension it can't be replaced, but works a damn treat!! Yes, the air compressors sometimes fail but so do other parts on other cars so to my thinking thats not a big deal. (cheap aftermarket kits are available to enable permanent height change/complete user selectable changes, and connection to a std compressor if there was a system failure)
Its also nice to drop the height, slide in under the caravan hitch and lift back up.
At the time, the LR was only a couple of thou more than the 550, but if wanted to start adding extras the cost jumps quick.
I love driving it (never thought I'd really say that about a car) and it is fantastic to tow with.
I won't comment on the Jeeps etc as I have no real experience there.