I don't exactly collect ereaders. I just keep them as I get a new one. I don't have anybody to pass them to. My husband got the first Paperwhite, but he doesn't need more than one. So they are stacked in the bookshelf with the books. Charged up once a month.
K1, K3, basic buttons, Voyage, Oasis1 and 2. I do not count any tablets/phone as e-readers as I don't read on those. I still actively use the Voyage and both the Oasisses. What the heck is the plural. Mostly the O2 and O1. Depends on where I am at and what is charged. I now keep wifi on all the time so they always sync.
Now I admit, I did keep the box the K1 came in, along with its cover. Just because it was so adorable and cute. Now they just slap them into brown cardboard. But the first kindle, oh it was such a joy to open that box that looks like a book. For nostalgia, I'll keep the K1 no matter what. Its getting a bit tired now, but still works. My precious.
So they just accumulate, rather than being collected. I guess that is just semantics. But if I were to collect them, I'd have bought every single kindle, or e-readers and I didn't do that.