Although it is not a practical consideration, I do wonder what would happen if everybody followed the nothing ventured nothing gained advice and sent cold the 'optimal' amount of cold solicitations. There would have to be a point of diminishing returns eventually, in aggregate.
Is this an important property of good advice - that people do not follow it, otherwise it ceases to be good advice?
No. While there is a subset of good advice which is only valuable because a lot of people don't follow it, that's not a property of good advice in general.
For instance, "Eat healthy food" is good advice, and doesn't become less good even if everyone began following it.
Marketing advice, though, is probably more susceptible to "becoming bad," since it typically depends on making your product stand out. Thus, as more people follow a bit of advice on how to stand out, the less this advice actually helps them stand out.
Although it is not a practical consideration, I do wonder what would happen if everybody followed the nothing ventured nothing gained advice and sent cold the 'optimal' amount of cold solicitations. There would have to be a point of diminishing returns eventually, in aggregate.
Is this an important property of good advice - that people do not follow it, otherwise it ceases to be good advice?