I don't have any AJ stuff, but I will keep my eye out for you.
Activities/games: Pin the Tail on the Pony!
I don't know what this game is called but it was my FAVE game at the church fair growing up: You have a "fishing rod" (stick, long string, with a clothespin at the end) and you cast your line over a large board (or a curtain, or foamboard, etc.). There's an adult on the other side of the board who picks a toy out and clips it using the clothespin. The adult gives a little tug letting you know you caught something! It's a fun way to give out party favors. I'm not sure how to make this pony themed, haha!
Design a Pony! You could have lots of arts and craft stuff and they can make their own customs! Either with a real pony or one drawn on paper. Maybe little jewelry boxes instead? They could be little gem chests!
Oh! Design a cupcake! They can ice their own cupcakes and throw on sparkly sugar crystals and candy and stuff!!
Ooooh, edible jewels! Stuff Spike would like to eat: Rock Candy Lollipops! I saw a really cool YouTube video for edible Kryponite...super easy to make and very festive! Change the colors and they're gems! Fast forward to 5:34
http://www.youtube.com/watch?v=h7xEB8o0Ez4Hoof Polishes! Or, rather, manicures with pony-colored polishes. Maybe do a little cutie mark nail art?
Oh, thinking of ideas is so much fun!