The only "modern" plate blocks I continue to collect are those with face values in excess of one dollar - especially the Priority Mail and Priority Express Mail plate blocks. This is more for the benefit of whichever grandchild gets interested enough in philately to warrant inheriting my collection. Filling in those missing high-dollar PBs many years from now could be prohibitively expensive.
In my opinion, collecting a "matched set" of plate blocks of a given plate number for a given stamp is one of the real "fringe" philatelic activities. I did it with my Farley's Follies PBs but no where else. I equate this activity with those who collect every possible plate number and/or position (or postmark) for a given stamp. You have to be a bit OCD to dive in those waters.