First of all, a spy camera is one you don't know about and can't see even if you do. Thus spy.
CCTV cameras are not invisible to those bothered to look for them, and are not secret; indeed often their installation is deliberately publicised
I don't follow the logic of an argument holding CCTV to be an invasion of privacy unless cameras used for observing traffic flows are also an invasion of privacy.
At this moment, as automatic number-plate recognition is developed software, and automatic facial recognition software is not nearly as reliable, I would say road-traffic CCTV is a greater threat to privacy.
The 'future government' argument is void; like a malign future government wouldn't do it anyway... "oh, wimpy past governments didn't install CCTV with face-mapping, and if they had we'd now abuse it, but as they haven't done it we won't" LOL
And of course whether CCTV reduces crime or simply MOVES crime is a moot question.
And whether any form of visual recoding will be admissible as incontrovertible evidence within a few years is also worthy of mention; give me enough of a budget and I could have the Pope and George Bush sat down to a dinner of baby brains, all through the magic of CGI.
Ask yourself; is the use of CCTV cameras to reduce crime functionally any different to a police force that had the luxury of putting observers in high-risk areas (which they obviously have a right to do)?
If it is (say due to the presence of a recording), can the difference be mitigated by legislation (say 7 or 14 day wipe-cycles)?