I'm 35 and am a keen collector of 1:18 scale diecast model cars. The sense of enjoyment for me comes from seeing their intricate details exactly replicated, from putting models from a similar age/brand/model next to one another and comparing them, from knowing that they can endure a long time without degrading and I can pass them to my son.
I fail to understand the appeal of "adult non-toy" Lego sets like these, however. It's impossible to replicate real-world stuff at any serious level of detail (the smallest brick is far too large), as mechanical devices they are flimsy (no greasing, no bearings, clumsily-weighed movements), separate sets do not stand well next to one another due to different scales and wildly varying subject matters. I do know that it is fun to build a Technic race car with steering, suspension, differentials and pistons, but such model-like stuff doesn't bring much value, IMO.