If one wants to put these old machines to good use, it's worth remembering (after checking that they still work), that these older machines (the iMac and the MacBook) are still user-upgradable.

The iMac should allow for 4GB of RAM (of which only 3 will be usable), the MacBook unofficially supports 8GB. Add in a cheap S-ATA SSD, and for some not too high, two digit amount of EUR or USD, these machines will be actually useful for someone.