I've always been surprised that people put so many books on their Kindles. I typically have 20 to 30 books on mine and when I decide I won't read one soon I remove it. It's easy to get it back.
I don't really do this for performance reasons although I'm sure I get that benefit as well. I do it to make it easier to browse on the Kindle for my next book. I know pretty much what's on board and where it is and I can go to it easily. And I do it because the Kindle is an ereader and not a hard drive. I think 1000 books on ny Kindle would make it seem more precious and less like the tool for reading that I want it to be.
It's your Kindle. Do what you want with it. It's my world and I'll feel free to laugh at you.
Barry