Where do I start on this BS?
1) 4.4 is an extremely reliable engine; the numbers and data are out there to prove it. Blaming a coolant issue on a spring clamp is hilarious actually because I'd bet my left nut that at 115K your hoses were probably still OG. Of course if you were following the maintenance schedule you would have not only performed the coolant change but you would have also (any real owner with the slightest of knowledge) would have inspected your entire coolant system for any anomaly's. That's how 95% of us find the real coolant issue which is the T-fitting and sometimes the thermostat housing bottom mate. Again, I don't care what vehicle, coolant hoses and brake lines have a life limit and should be followed. If that clamp did fail, it should have been found during your inspection, don't blame LR if they didn't look at it. Every 12k miles and more under Severe Duty use.
2) Lackluster interior and quality: The LR3 was arguably the last utility variant JLR built. The interior was lightyears ahead of the Defender that was coming off the lines and nobody seemed to care; to say lackluster is relative to who views it and their purpose for it. Keep in mind, almost every component is designed to pop on and off to include the breakaway clips on the bumpers; not sure where interior quality has been an issue with most as I have not experienced this or read this much of anywhere. With the exception of the 8 million screws holding the dash on (Dash cover airbag cracks are a big issue) the rest of the interior can be taken out in about two hours mostly by hand and the rest with two tools. LR4 changed in that aspect as the interior became mainstream and elegant which in turn needed more sound proofing and tighter securing. The LR4 can be had now for $10-14k so look around cuz there are some great deals. Keep in mind timing belts on the LR4; I know they are out of the current budget but just throwing it out there.
3) Yep, she's heavy, built well and extremely survivable in every situation. Can't remember how many airbags that actually work in a Land Rover but they didn't seem to get the same heat as the millions of Toyotas that were pulled for safety not once but twice. Anywho; that weight is a tax in trail mud and gas mileage only but safety, comfort, and ride quality to include off-road. I rear ended a Camry at 15mph and the LR3 drove away to clear the road and the Camry's trunk was in the back seat. I'll take that weight for chassis strength and safety both on and off road over the GX. Google Land Rover and Audi on the Autobahn. When I am in my LR3 I feel 100% safe and the data proves that as well.
4) Water Pump Failure: not sure what the mileage was on that but sounds like someone maybe had some significant coolant issues or lack of care involved in the coolant system like highly corrosive neglect of internals and external components. I did my water pump at 75k because I had an accident; not a hint of a leak. I don't see a bunch of water pump problems listed in the forums at all but I put a Delco one in over the LR one due to cost and over 50k miles and still running leak-less like a champ; maybe someone has some further data on that but I did two water pumps on my F150 and Excursion and my Lexus had one (under warranty 52k miles) in the time that I "didn't" have an LR3 water pump failure.
5) Use JLR factory tail-light bulbs or upgrade to LED bulbs ($50) or LR4 taillights and all of these are solved. Store bought taillight filaments are not vertical like JLR bulbs so when they fail (JLR bulbs rarely fail but they do at times like other lightbulbs) they short-out causing the top and bottom filament to touch; this trips the ABS to think the vehicle has an issue and it goes to limp mode. Again, use JLR vertical filament bulbs or LEDs and you will not have to worry about this problem. Carry spares like you should in all vehicles. Are there some air suspension complications; yes, but generally speaking well maintained you will have little to no issues and you will see this argument all over the forums. But, on that note, for the cost of rebuilding your suspension that will likely need it at high mileage anyway (all vehicles have condition based suspension repairs) you can install the AB OME coil kit and all of your EAS worries are solved. I would say its like adding Bilstein upgrades to your GX
6) Water intrusion issues come from the moonroof drains getting clogged. I've heard of a few cases were the interior drain tubes have broken but I have not witnessed this. I've had many cars/suv/trucks with moonroof drains that needed to be purged/cleaned out, multiple OEMs. It is true if your LR3 drains are clogged they will leak down into the kick plates where there are wire looms and will cause corrosion. Light compressed can air you can easily blow these out on your periodic maintenance schedule.
Just wanted to provide some clarification for the overwhelming amount of LR3 owners and lovers that properly care for our vehicles and not put you in doom and gloom mode like there are tons of problems and the thing just blows up because it's just downright untrue. I just don't think the LR3 or the GX are get in and go vehicles like there are no maintenance considerations on either platform. The OP clearly states he plans to use it for an overland build. A properly maintained vehicle like the GX or LR3 will give you high mileage joy and excitement if you put the effort in on your end as well as both vehicles in this environment will need proper and regular care.
@johohoward Sorry for the novel but feel if I can help provide good and constructive information to help on your decision than I've done my part in what you asked of us readers. PM me for any questions directly if desired. I do not have any GX experience but the neighbor up the street has one and I can research some points if needed.
Ciao