I have been collecting postcards of my home town. Mostly I buy them on ebay and have more than a hundred now. I particularly like the used ones. There's something rather special about letters written more than a centruy ago.
I don't collect them in an organised fashion but if I see one that I like or that is of something meaningful, then I will buy it and keep it. I sometimes come across one or two when I'm looking for something else and it gives me a minute or two of pleasure looking at them.
I've just joined the website 'post swapping' where you automatically get the details of someone overseas to send a postcard to, then once it's arrived and they've registered it on the site, someone else will get your details to write one to you. Done 4 and got 4, so far.