Bdub- Take this with a grain of salt - just totally my opinion. Do you really want to be dealing with receipts with her for the next 8 years? Is there a way you guys can come up with an annual number that she can operate with (can always be adjusted for cost of living increases)?
In my situation we are splitting the cost of extracurricular activities and any medical bills that my insurance wouldn't cover and that's it. I'd pull my hair out having to bother with receipts with STBX all the time, but thats just me.