I must admit to never hooking into the appeal of collecting plate blocks. These used to be the corner block of four with the printing plate number. Then for a while they became the entire side of a sheet of stamps, usually two rows adding up to twenty. There are also variations including 6, 12 and 15. It seems to me like preferring to buy newspapers or magazines before the edges are trimmed. "Oh, look at all the pretty colorful printers marks!" On some plate blocks there are pretty printers marks. But the earlier plate blocks have just a simple number that was assigned to the printing plate.
For years issued as plate blocks of four, if one looks around many going back fifty years and more can be found for sale at face value. Many are still used for postage, though you have to have a pretty big envelope to fill it with the proper postage when you're using 3¢ stamps. Collecting the current self-adhesive stamps in the plate block format brings a whole new set of problems. Ideally the stamps backing paper should be die cut for easy separation. But that is not always the case. It just seems to me that if you like a stamp, buy the stamp -- not multiples. Of course, in stamp collecting, like everything, else de gustibus non est disputandum.