At todays council transport committee meeting there was an item on how the parking wardens work. (full report - section 7.5 http://www.edinburgh.gov.uk/meetings/meeting/3632/transport_and_environment_committee)
In the appendix there's a schedule of how often the wardens are required to patrol each area. Must say I'm very surprised at how infrequent they're required to patrol.
The report also mentions the income to the council at £14 million per year. That may include parking permit, parking meters etc and exclude the costs - line painting, maintenance etc.
If it is genuine "profit" I don't see why the council doesn't increase the schedule?
Parking Enforcement schedule - City Centre by fountainbridge, on Flickr
Full schedule - https://flic.kr/p/qHRR9Z