See, but then you assume that such things as curiosity & wonder would dissipate over centuries & millenia, but I beg to differ, even now, on a small scale, we can endure repetition with ease, we can even find comfort & solace in it, yet, even in our repetition of particular things, watching movies, roller coasters, love - we experience something new all on its own in a way we can't describe.
Each experience, each discovery, & each activity is its own thing, even upon repetition, & at times when we do feel something is repetitive, if we abandon shortly we often come back to it later with a newfound fondness, a new emotion & different thoughts & we ourselves are different people then.
Our world is so incredibly dynamic, in nearly every aspect, that I don't believe the human brain is completely capable of getting tired of it, because it's never the same & it's always wonderful in its own way, only when you generalise experiences together do they those their significance & potency.
I think there are many different things that could motivate & interest people, I think death & fear of death is only one, and definitely a strong one, but not the one & only prime motivator of action & all, especially for human beings.
You yourself are not indifferent to your past, your recollection remembers the experiences of your life & how they affected you, why would more years change such a thing? Older people don't show signs of indifference to humans as a result of experience, that's not a huge or significant trend, so why would arbitrarily more years cause such a thing?
I can see the ocean or a beautiful woman & find it all the same beautiful as I did before (affected somewhat maybe by my hormones & the like), why would the world lose its beauty or mystery after having seen it so much? Plus, it's always changing, & so are you, & everything in the world.
I just think humans & most things concerning them are incredibly complex, so I think there's any sureness of what a millennial life would be like, but I think there are so many things it could be, I think negative would only be a small part of it.