This was fun and enjoyably light on the unneeded scenes. If any further development was wanted, I would recommend only an epilogue to explain any nifty differences that you'd like to play out. Hermione's dosing I would attribute to Ginny trying to direct her away from Harry as her relationship with him is the greatest threat to her master scheme- if Ron had used a potion on Hermione, he wouldn't have been bothering with Lavender.
I have actually seen a reference to the Inigo Montoya bit in the chemprof story on ff.net called 'Hermione's Plan', though Harry didn't actually say it to Voldemort; he just teased Hermione that he was going to do so. Excellent usage, nonetheless!