This is were things like browservice comes to the rescue if you have a bigger machine available and only need more independent terminals:
https://github.com/ttalvitie/browservice
Also rdp/freenx/x2go/vnc can help.
That doesn't make the old computer a full independent desktop but it can avoid sending a perfectly good keyboard/trackpad/monitor in the landfill. And unless you are a dev, 99% of the time you need a browser you already have network and won't point to localhost so that remote faster box can be connecred through vpn anywhere.
Also rdp/freenx/x2go/vnc can help.
That doesn't make the old computer a full independent desktop but it can avoid sending a perfectly good keyboard/trackpad/monitor in the landfill. And unless you are a dev, 99% of the time you need a browser you already have network and won't point to localhost so that remote faster box can be connecred through vpn anywhere.