If they are truly dead, then what else are you going to do with it?
If it is "dead" because of new technology, then you can keep it around "just in case", or give it someone who can use it.
I had an old HTPC built around an Athlon XP 2600+ back in 2002 still in working order. I was trying to give it away for free from 2009 until last month. I ended throwing it away because I was moving and didn't want to bring it along with me.
I also have an old IBM ThinkPad T40 from 2003, but I'm keeping that. Nostalgia I suppose and it doesn't take up much room.