I also wonder what to do about the 150 articles on article sites I posted 2 years ago - whether I should delete them or leave them.
As matinibuster suggested above, "that can be troubling." We can't be sure, but those sure as heck seem to be the types of links Google is now targeting: those built to manipulate PageRank.
you are admitting guilt
Sure, Google's already caught the person with hands in the cookie jar, that's why the site has been dinged. The disavow tool is supposed to be used for spammy links that *you built* (or have had built), and have not been able to remove by normal means.