Whitehats can benefit greatly from selective grayhat tactics. I think a lot of secrets pertain to getting links in different ways, so unless links in general become worthless, I don't think you can make a statement that all gray links are useless. There are other "questionable" tactics beside linkbuilding that have been making people a lot of money for a long time (just check the top results for many competitive queries) and laid the foundation for entire businesses. You just have to be smart/selective about it.
I personally don't like the answer "if it's spam it's not worth knowing" - it certainly has been to some.