I also worry it'll be fun for a few hours before it turns into a grind-fest
I'm hoping that because every planet is so unique, that this will not happen, and that you'll always want to come back for more, wandering what else you'll find on other planets
Elite doesn't have that, as you can't land on planets (yet), and each star system, although slightly different, feels quite similar to each other.
So in my eyes, No Man's Sky will be a more interesting version of Elite with a lot more to do - but that's how I see it for myself. Elite to me looks and feels like it's trying to set out to be a space sim dedicated to being as realistic and authentic as possible. No Man's Sky however is looking to be like it aims to be solely about scale, freedom, exploration (even though you can choose to focus on other activities) and imagination.
The cartoony graphics are a clue to this I think, opposed to Elite's realistic, life-like graphics.
So yes, it's looking like No Man's Sky will have it's own niche to fit into...I hope.