Good analysis overall. I'll add up a little by my own game experience.
Ambush (in my case 1x): even conditional, having a single card lets you have it in hand and create great swings in combat. It may seem overkill, but using it to break/defend a capital o a key conflict can turn games. It's earning a 6 fate equivalent boost for a cost of 3. Even if it looks situational, deploying a cost 4-5 characters plus a weenie is quite common. It's specially good when attacking/defending with a cheap character and your opponent wastes his bowing/dishonoring stuff on him.
Blackmail (in my case 2x, could also be 1x): the chance to turn a probe attack in your favor and claim the ring is priceless. Particularly flashy if you reduce the cost with city of lies. It's specially effective against characters like Brass Samurai, since you can take control before it gets honored. It's also brutal when taking control of a courtier and combining it with Spies at Court, or use it to dump any other dishonoring efect with the Rumormonguer.
Court Mask (i'd say x1 or x2): This cad got clogged in my hand when I ran 3 copies. But playing just a single copy can help freeing your deck for more spaces while benefiting from its comination. The most important part is that dishonoring is part of the effect, not the cost. So it could be activated when attached to an already dishonored character.
Favored Niece: don't let the stats fool you. When I started to run the deck with many 1x and 2x copies, this character became a cycling monster and let you always have the right tool in hand.
Shosuro Actress: can attack/defend a political conflict, get discarded and bring a readied military character from the discard pile for another conflict. Cheesy if timed well.
Shosuro Illusionist: Stats are incredible. Very few characters have a value 3 raw stat for cost 2. And the skill is extremely useful overall.
Would you consider the Magnificent Kimono in a Phoenix spalsh? The extra honoring is very useful to pay dishonor costs. A Hiroue or Shoju with one of those is scary. Even if it eventually backfires, the Illusionist can prove useful. And it's another buffing utility to ensure a province breaks.