yea the main thing that I was hoping to solve by using the audio setup vs serial or icsp is that end users would not require any extra hardware and reprogramming would be extremely simplified since they would not even have to use the arduino IDE or anything since one could simple send out the audio file and people could update their devices. ICSP requires either an arduino as ISP or some external programmer which is added cost. And ftdi, although integrates the hardware in to the final product, still requires someone to use the IDE/avrdude to reprogram the device. Overall, although insigificant for someone experienced, for the nontechy these methods of reprogramming are bit more confusing.
But you are correct in that the devices will not be programmed that often. I mainly want to keep the option open just in case there is a patch that needs to be deployed or updates to code over time.
Also, can you trim the reset button off of the ICSP and just require a manual reset press? This would allow one to wire the ICP pins into say a microusb port which would be alot nicer than the current interface.