"...what can I see on Google that I can't see from the street?"
If you are about 2.5m tall.
" The resolution and detail are crap, you could certainly do a better job of casing the joint just by walking past the house in question."
That depends on how close the house is to the street - some Streetview images have enough detail to identify the presence and type of window locks, the presence of alarm sensors, etc. Taking a good look at the security arrangements for a house in person is likely to attract attention from local residents.
Google have been fairly sensible in giving people the option to decide whether their own property should feature on Streetview.