No one really asked, but here's my philosophy on the subject.
To begin with, I 100% agree that plate block collecting has waned and few of them from the 1940's to present day have much of any value over face. However, having said that consider the following:
a. More and more collectors are tearing plate blocks up and using the stamps for postage, which to me means that in the future the availability of plate blocks will be proportionately less and could mean that prices will go higher in the future if there should be a recurrence in demand for them (admittedly a long shot).
b. Sometimes a lot of postal history can be told by identifying the plate number upon which the stamp was printed. How much more space does it really take to store plate blocks as opposed to four single stamps? Until you need to have a supply of single stamps, I would lean toward leaving them as plate blocks. You (or another collector should you sell or trade them) can always tear them apart later on. Once apart, though, they cannot be put back together again, so the value of the plate block, however minimal, is completely gone should you just tear them apart now for no good reason.
c. Fast forward to 2012 and the plate blocks of today (often in four corners of a sheet of 20) are a lot more common than the older ones where there was only one plate block for every sheet of 50 or 100 stamps. In reality, plate blocks today are not really necessary with computer-driven printing equipment, so they really stay on the stamps for die hard collectors (who, of course, add to the revenue of the US Postal Service by continuing to buy them). If you absolutely must tear the stamps apart, consider keeping the plate number "singles", that is the single stamp with the plate number selvage attached. Apparently this is becoming quite a popular sub-collecting discipline and, as was said earlier, if the plate number stays with at least one stamp, you may be able to identify a whole lot more about it than just seeing the stamp alone. Consider some of the other reasons for collecting plate number singles at this link:
http://www.apnss.org/intro.htm