Are we caretakers for another generation?  

U haul
I've never seen a hearse with a U Haul trailer behind it...
we always pass it on to someone!

I feel like a custodian of a beautiful object rather than the owner as the piece has its own journey and I'm just a part of it. I grew up with antiques and watched beautiful things come and go all the time. I guess I was never destined to buy new stuff which is good as taste evolves and what I bought ten years ago I would not buy now and I imagine it will be the same going forward with some items traded out to be replaced by better pieces.

Everything we do now is left...
Everything we do now is left for a future generation to deal with. Everything. The world we live in today has been made possible by all preceding generations combined. I call it the giant snowball of humanity. It has the potential to grow, or melt all because of the choices various generations have made.
Directly addressing your question, it isn't one dimensional as ownership or caretakers. It's multi-dimensional. My choices today may not be full considering my future children...but I do realize that my choices will affect their perception of world and the world of design. What they decide to do is up to them. Parents have one of the most important jobs, to help future generations make good sound decisions. I say help instead of teach, because what we teach isn't always right.

Yes, we are
but not of stuff, of the planet. If we put that first, then good care of stuff seems a logical next step.

Beyond our stuff
I think that most people on this forum would put the welfare of the planet and humanity ahead of their stuff, but I would argue that our recycling of stuff is indeed good for the planet and it's people. Almost everything in my apartment is secondhand, from cutlery, plates, glassware, rugs and furniture. Even my t.v. Is a hand-me-down.
What interests me is what drives our passion for design and vintage furniture?

Yeah,
that's what I just said. I agree. Recycling, reusing repurposing... all of that is goodgoodgood.

I also like the idea of...
I also like the idea of recycling/reusing, but ultimately I just enjoy vintage things far more than new ones, and always have. I like that they have a previous life, I like their patina even if means some bumps and bruises, and I like that they are truly original pieces. I also like thinking that something of very high quality will be cherished for a great many years, and is the opposite of our culture of disposable "stuff". I am not the first owner of any of my furniture, and I really hope I'm not the last, either.