Not more data, better analysis
They should be concentrating on dealing more effectively with the data they already have, not trying to add to it.
The haystack is big enough already, they need more people with magnets to sift through and find the needles.
And then, they need to use that information appropriately, not keep it secret. Once again, it appears, the security services were aware of at least one of the Brussels attackers, but they didn't release that information to the people that mattered.