After 8 months of trying, I finally got listed on Yahoo!
One thing I did was clean up some dead links and broaden my link page. In the description part of Yahoo's application, instead of telling what I do, I told potential viewers about the free newsletter, free samples and link page. This is all advice I got from this very site!
And in what may have been the coup de grace--I added Yahoo to my link page. I wonder if this could have made a difference.
One more thing...I learned from this page that Yahoo won't list 2 sites from the same sub-domain. But months ago they listed my newsletter with the address http://www.tp.net/tp/users/formichelli/wordwise.htm (though they buried it under "Education"), and now they've listed my main page with the address http://www.tp.net/tp/users/formichelli, 8 months later. Maybe they're slipping.
Thanks everyone, especially Jim, for posting such great advice!