Nice stuff man, way more to sculpture than just making bongs. You get as much out of art as you put in. Weather its on your own or in a high school ceramics class.
Check out Mike Simi's work for some interesting ideas. You're nikes remind me a lot of this work of his: http://www.mikesimi.com/detail%20pages/Nike%20Dunk%201.html
Maybe look into slip castings? Making molds of objects and turning them into a clone copy in ceramic is really cool. Also you could experiment with bizarre methods of glazing pieces. Soda firing.
Have fun with it dude