(I fully agree with your point; however, I'd argue that the (relative, back then) lack of digital storage and communication made gathering of information much, much harder back then than it is now - even for the Stasi.)
Fun-fact: The Stasi installed Caesium-based gamma ray scanners in some border checkpoints. To this day no one knows for sure how strong the radiation exposure was.
So they needed to make sure all the people expected to be under surveillance all the time, to keep them from doing anything undesirable (to the state, that is) while not being watched.)
IIRC the Stasi had a hard time connecting the dots (pun not intended) as the massive data sets mostly existed on file cards.
Today's problem is somewhat different: You've got loads of data, you've got the means to rapidly search and index it - but still, for some reason or the other, massive data collection doesn't appear to lead to much by way of desirable (to the populace, that is) results - actual terrorists apprehended, actual conspiracies unearthed, etc.
A cynic would assume that means the data is collected for other, more nefarious purposes. Cough.