The trouble with this formulation of when surreptitious methods are acceptable is that the determination of what constitutes "information vital to the public" is made by journalists looking at the world through deeply liberal-tinted glasses. Any level of subterfuge and deception would be deemed acceptable to, for example, dig out dirt on Sarah Palin, but most of today's journos would shrink in horror at the thought of using such methods to try to get access to Obama's college records.
Frankly, looking at most of the practicing journos today, I find the term "journalistic ethics" to be an oxymoron.
As they are ADVOCATES not journalists.
Here's a good site to drive home that point.
SEJ: Society of Environmental Journalists "Your source for environment, energy, science, health, and climate reporting"