If the NSA revelations are anything to go by, the only difference between "not enough data" and "too much data" is that the after-the-fact investigations are now a bit easier.
There doesn't seem to be a "Goldilocks" amount of data. Or if there is, intelligence services seem to have no interest in finding it if it means restraining themselves.
Alas, the spying is apparently targeting mainly the innocent civilians and is mostly ineffective against criminals.