Some of them are very good for pet projects and hacking and rooting and doing stuff you would not dare to do on your new phones. I would love to tinker with them a bit.
I only have one outdated smartphone, bought about 2010, and discarded late 2015 simply because the USB charging mechanism was too worn out (could have got that fixed, but wanted Android 4.x which it couldn't do); was on its second battery. It now sits peacefully in my desk draw at work.