If you want the car, you have to jump in sometime. If you are happy driving whatever you have now, keep driving it. I am confident that each additional year will result in lower E9X M3 prices. I wanted a newer car and wanted a CPO with 3+ years of warranty, so I bought one.
If you want a more depreciated car, buy an E46M3 or E39M5 or early E60M5. All but the later E60M5s are out of warranty now and I am not sure I would want to own the E60M5 out of warranty.