If someone will buy the printers for weight, its better than nothing if you get them for free, and you don't have to do anything.
As for the PCs, missing ram and HDD devalues it since you really only have the motherboard, cpu, cd drives and power supplies. Since they are free, I would take them anyways, they are pretty easy to take apart, maybe 5 min apiece? Especially once you get in a routine. If you get them, separate them by brand and you will go alot faster once you start breaking them down since you will get to know where all the screws are