I say you need to think about this a bit more
Yes, it is, in theory, useful to have a gigantic database that you can /just/ pull out /just/ the right data to simply solve the crime you're trying to solve. If only you /just/ knew /just/ what to pull out of that database, silly. And in the meantime it's a big fat threat to privacy, safety, and freedom from government bother, to everyone including the big majority who have not and never will done anything wrong.
That means that data retention is /just/ Not Worth It. Even if in the far or unlikely near future your vaunted all-solving new vapourware will suddenly become less vapour and actually somewhat useful. You're basically touting "Total Information Awareness" for use against all civilians this time.
The thing isn't that retaining all data on the theory the right stuff you need is in there somewhere is suddenly feasible so you can conveniently gloss over whether it is desirable. The thing is that even with the best of the best data mining apps ten years down the road it's still an unwieldy moloch and threat to civil society, stasi style. Some of us have been there and have learned. Some of us, clearly not so much.
What you do not need is heaps and heaps of tech and a good filtering app. What you do need is to very precisely know just what data you need, where and how to get it, and how to make sense of it. Then you can go about your crime solving business with maximum effectiveness for minimum privacy invasion.
You know, the reason why there's such strict controls on police powers is exactly to try and protect the innocent majority from privacy invasions necessary to dig out the criminal very few. This here data retention is about maximum privacy invasion inevitably, logically, necessarily resulting in minimal effectiveness. Is that what you really want?