If you have a use for it, I'd just clean the rust off it. Maybe refinish it if you want it to look pretty. As a general rule, if an item has severe finish problems as this one does, you don't hurt the value of it by restoring it, unless it's something so rare and desirable that buyers will pay good money for it just as it is.
I've found that with most vintage woodworking tools, the value is intrinsically linked to its functionality. Most folks buy vintage woodworking tools primarily to use them, not to collect for display. If it can no longer be used effectively, it usually doesn't matter how old or rare it is, it will have little value. Roached and rusted finishes against bare wood is not usable.