If 1 year old 8 core 8GB boxes are only going for $400, what can I do with a bunch of 3 year old 2 core 4GB boxes, where it's making more sense for me to replac

If 1 year old 8 core 8GB boxes are only going for $400, what can I do with a bunch of 3 year old 2 core 4GB boxes, where it's making more sense for me to replace them with newer boxes that use less power and space?