I think that variety matters. Different props and different plots. You are better doing tricks with cards rather than card tricks that is, tricks where something happens to the card (torn and restored, vanish and reappearance, etc.).
You also need "something more" that gives the effect sufficient substance and allows for a good presentation. For example, I do an Invisible Deck routine that uses a beach ball and some music. The music starts and I toss the ball to someone who throws it to someone else. When the music stops, whoever is holding the ball names the color (red or black). The music starts again, the ball gets tossed around and when the music stops, someone names the suite. Repeat for whether it is a face card or a number card and then for the value. That keeps you from doing 25 one minute effects in a half hour show. Each effect should be 3 to 5 minutes or longer (my average is 6 minutes for 10 in an hour show).
Remember, that these parties are typically parlor style magic and not close up. Pick effects that work for that type of show.
No. The 8 year olds might laugh, but the 11 and 12 year olds will think you are lame.
Feel free to post your set list and I'm glad to give you ideas.