If we decide not to allow the public to fly drones around peeping into back yards, the same should apply to the police (without a warrant). The limits on casual/easy police surveillance should be pretty much the same as the limits on the public. The police should be no more than citizens that we have authorized to act in our name.
That said, it may be time to be realistic, that technology is expanding our powers of easy observation beyond historical limits. Create new laws regulating personal and commercial drone camera use, including allowable flight altitudes, linger times, recording and viewing resolutions, etc under various circumstances - with the same standards governing police use without a warrant. Balance new benefits against the loss of a few old privacy benefits. Same goes for things like Google Glass.
The key is to avoid allowing politicians to carve out any special exceptions/powers exclusively for the police - insist that police powers be based on those of the general public.