Star trek is pretty cool.
Most of the things you can learn from Buffy are similar to things you learn from other tv, it's just that the examples are different.
The entire story arc for one is a lesson in sacrifice. Sometimes to do the right thing, or to help the people in love you have to be willing to lose the short term bliss that you may have.
In the season 2 climax "the becoming 2" Buffy is forced to kill the once more good Angel, whom she loves deeply. If she hadn't the world would have faced an apocalypse.
At the end of the 5th season, she must throw herself off a tower through a portal to close it. Doing so spares her sister from having to do it (only the blood of the one who opened the portal can seal it), and once again saves the world from being sucked into a hell dimension.
The end of Season 6 shows us what it means to love. Willow, bursting with dark magic which she absorbed, seeks to end the world to stop her own heartache. Xander, who has no special abilities is left to save the world, and does so by reminding willow of the love that he has for her as his oldest and dearest friend.
My explanations may not be particularly good but I believe as Christians, regardless of age can learn from the actions of others, be they made up and in a book or television program, or real life people, making the best of the world we live in. I also think you can learn from Christian and non-christian alike.