However, I think that your average smash and grab robbery, at least in the UK, is usually handled by the insurance companies rather than the police. The police provide a crime ref so you can claim that it is a crime and that's it. There's very little prevention or follow up done.
I doubt it'd change that much if they deployed it here.
You could offer it as an easy to use app. The would-be criminal sees an opportunity, pops out the cellphone and gets an accurate estimate of how likely it is that a cop will be around for the next couple minutes. Premium subscribers will also get advice on which possible crimes would be more profitable and likely to suceed with present police force deployment anneighborhood demographics.
Any real-time neighborhood safety app that relies on the same data the police uses (or a similarly complete dataset) intended for mapping areas suitable for, say, nightly outdoors activities, can be used for avoiding police.
The second part, I agree, is completely criminal. I doubt it will become available on any mainstream app store.
I would be very surprised. Most criminals are stupid and have poor impulse control (so elaborate planning is out of the question). While the brighter and more determined ones are unlikely to be interested in burglarising your home or tagging an overpass when they can be dealing drugs or slinging guns.
I heard a couple of cops mentioning that people ask them what the best places in a city are to buy drugs, or pick up hookers etc. They really don't know! They only know the best places to get caught for that stuff :)
Most of the data they use is probably available to the public already under various open data schemes, so it's only a case of wiring it up.
It'll turn into a game of cat and mouse like SEO is for example.