Slayers
I don't think that Buffy and Willow had "created" new Slayers, like the Shadowmen of "Get It Done" did. Those girls would have eventually become Slayers, via the death of previous ones - starting with Faith's death.
What Buffy and Willow did, I believe, was change the system of Slayers. Instead of one at a time, coming into the fold (and being controlled by some kind of Watchers' Council), any Potential around 15 years or older, immediately became a Slayer. Not only that, I believe the Scoobies will try to contact these new Slayers and give them the choice to pursue the duties of a Slayer . . . something that Buffy had offered to the Potentials in "Chosen". That is why the Potentials, who were previously hostile toward her, were willing to fight by her side in the Hellmouth. Instead of forcing them to fight, Buffy offered them the opportunity to make a choice. Kennedy, Rona, Vi, Amanada, and the other Potentials in Sunnydale and throughout the world were eventually going to assume Slayer strength. But what Buffy and Willow did - and plan to do with the other new Slayers - was give them the choice to act as a Slayer.
I also believe that it was female empowerment that saved the day. Only it did so, through Spike. Empowerment does not always mean "kicking ass" via physical violence. There are other forms of empowerment. Empowering others through compassion, tolerance, emotional support and love. And this is how Buffy defeated the First Evil's plans - via her emotional support and feelings for Spike. Can you imagine what would have happened if she had never been able to forgive him for what happened in Season 6? If she had not given him the chance to forgive her? Or if she had not told him that she believed in him in "Never Leave Me"? Buffy had defeated the First Evil through her compassion and forgiveness, the same way that Luke Skywalker had defeated Emperor Palpatine in "Return of the Jedi" - via his compassion and forgiveness toward his father, Anakin Skywalker.
I believe what Joss Whedon was trying to tell us that a woman's (or should I say, a person's) greatest strength is not through brute strength or physical violence, but through human emotions and the abiilty to connect with others. I think it is a great message.