Whats considered a collectable computer

I think it would be a very interesting discussion to see what everyone thinks is collectable.Personally I am trying to limit my computer collection to only Pre-DOS machines, like Kaypro's, Osbornes, and mostly Home computers of the late 70's and 80's like Radio Shack, Apple, Commodore, Texas Instruments .. I believe that most any machines after the IBM PC-XT will never really gain any value, Well maybe in the year 2050 a Pentium will be quite an interesting antique.. I do have several Portable DOS machines in my collection like the First IBM XT portable computer, The first Compaq Portable XT, Kaypro 16 XT Portable, and I also have 2 Columbia portable XT's. I believe that because they were considered portables that will make them unique and collectable.. Funny how many Sinclair computers there were in the 80's. I used to see one at every yard sale for years at a dollar or two, now these computers are never to be found, and those I see on eBay are getting an unbelievable price.. Phil...