You can get an LPG conversion at less than £2500, and the saving on fuel is well worth having, you'll average the equivalent of about 26-30mpg on LPG. Planning trips to include LPG stations is no hassle, and more are being added. We did 1500 miles to John O'Groats and back in September, and had no big problems, even in the Highlands. You DO need a gas outlet map/book though. Once north of Inverness, Dornoch is the last gas point northbound.
Whether it's worth it is entirely your choice/decision. Ours was bought with a Zavoli multipoint system fitted, we targetted an LPG-fitted V8 as we weren't that keen on another diesel after years of diesel vans etc. Ours is a 5-speed manual, most are autos. we tow a lot so wanted/preferred a manual box.
Gas is 56p a litre locally, we get 14-15mpg on gas on our Disco 2 V8, you can work out the figures.
In some respects the V8 petrol engine is less hassle than the TD5, but the older Disco 1 300Tdi was reckoned to be better than both.
A good V8 is a lovely car to drive, but a thrashed V8 with gasket or liner trouble is a money pit. A TD5 with a broken dual-mass flywheel or a cracked head is also a money pit. Mechanically they are the same apart from the engines.
Servicing is no different to petrol or diesel-fueled vehicles.
You pays your money....
Peter