It's a manual transmission luxury SUV; a market segment that does not exist anymore. It has a massive aftermarket for engine and clutch parts, and it has many parts that interchange with other BMWs. It's from an era that I see as having been the perfect blend of simple old-school engineering, and simple but extremely capable electronics. And due to its age, every issue and electronic module is well documented and can be recoded and reconfigured.
Seats from various BMW chassis will bolt in (E46, E85/E86, E63, maybe more), E38 and E39 use the same gauge cluster, the engine was present in just about all of BMWs model range from that time and can even be replaced with a 2.8l iron block from 96-98, and the Siemens MS43 engine computer has open source tuning software available for it.
It's also one of only 1079 (if I remember the figure correctly) 6-speed manual X5s sold in the USA. Keep it. It's a special vehicle.