The "good enough" concept is valid and important in many areas, including product management. There is never a perfect product, so a good product manager knows when the product is "good enough" and ready. This is based on many factors, such as customer feedback, quality, R&D reality, roadmaps, competitive data, etc. This subject is taught in Pragmatic Marketing and is widely used in most PM organizations today.
But does this principle work in other marketing areas? Not in my experience. For example, the difference between "good enough" and great for PPC and SEO is drastic. Lots of PPC campaigns never work and exec teams stop believing in these as valid lead gen tools because marketing never puts the right level of effort on finding out what are the exact keywords their prospects use at different buying stages, from the research to purchase. This is not an easy process. And good enough usually = failure. This is where you use "Hack Marketing" to find the right keywords. The results of these extra steps are the difference between success and failure of PPC and SEO.
The same goes with the rest of messaging. It really pays to conduct research and understand what are the exact words customers and prospects use. There is no "good enough" here. For example, we changed one word describing how the product category is referred based on customer feedback. Lead gen campaign results shot up 67% in one week.
Finally, "good enough" marketing materials in my experience are useless. I rather have a great web site with all the right messaging and use it as the major marketing tool instead of tens of mediocre white papers just because it is "the right thing to do" and "everybody does it."
So is "good enough" marketing good enough?