After many difficult days of dealing with mysterious problems paring back my library, I've finally hit on a winning combination. I had tried many workarounds posted here and elsewhere and though I got my library down to about 23000 I still couldn't get Match to work; that's what I meant by mysterious. I tried simply changing the Media Type, and though the track would show as Ineligible it did not affect the 25000+ count (presumably because the file was still in the cloud even though the local file was ineligible?). So then I went the route of exporting thousands of songs I could live without, and deleting them from the main library. Match STILL showed I was exceeding the limit (with 23K songs!). Finally I realized that I had other computers that could both see my local files and were using Match. So, though I was culling my library on my main machine, the others were keeping the songs live on Match.
My ultimate fix was to turn off Match on all my devices, and then I deleted all the iTunes libraries on my secondary machines since they should be using the music in the cloud (or via home sharing). I disconnect my external drive where my music is stored, and then start Match again on one of the secondary machines with a new, blank library. iTunes will show the "cloud download" icon for all the matched and uploaded songs. I then selected and deleted songs that I do not want in the cloud (low rated songs, high skip counts, certain artists and genres, etc). When you delete them you will be asked if you want to "hide" them in Match; you do. Now, when you open your main library, those deleted songs will show as "Removed" in the iCloud Status column.
As an aside, if I want to add new music to my local library but not to the cloud, I turn off Match before I add the music, and then turn the Media Type to Voice Memo, and then turn Match back on. Those songs will show as Ineligible. I know some folks use Podcast or Audiobook instead, but using Voice Memo allows the songs to appear with the rest of your Music instead of a different window.
Also, to keep vigilant, I created a Smart Playlist that shows all tracks that are Music and are either Matched or Uploaded. This allows me to see just how close I am to that 25000 mark. This list, obviously, excludes Purchased, Inelligible, Duplicate and Error tracks and also all those "Voice Memos" that you did not want in the cloud.
Why Apple can't give us a simple "Include" flag and allow us to easily choose which songs are Match'd, I'll never know. Anyway, I hope this is helpful to some other struggling souls!