Basically, people who buy diesels generally like them.

They won't save you money vs a 35i, due to their lower reliability and extensive issues with carbon build up and emissions failures. Most diesel owners exaggerate their fuel economy results, they are real world about 10-20% better than the 35i. The 35i is faster and quieter and has more hp. The 35i is really the low cost option on an x5. Generally I'd say the diesel and the v8s are equally as expensive to maintain. There are lots of mods for all x5 engines, and most of the emissions problems can be fixed by modding, if you live in a non emissions checking area.

I own a diesel, and like it. But it's had extensive problems with the emissions and after spending a lot to remove them, it's finally reliable for a BMW. Some people are lucky, but hey not every 48i has bad valve stem seals and a valley coolant leak right?

With that said, I never bought another diesel after this one, thought about one for my x5, but opted for a gasoline v8 which has been more reliable than my diesel. Both 48i and x5m have had fewer engine issues than my 335d. But I love my 335d and drive it frequently