Like most treatment modalities and diagnostic protocols, the Vega machine has some use. Although it has been claimed to be an accurate diagnostic and therapeutic tool (even claiming it can cure cancer), I find it most useful for the measurement of electrical currents in the oral cavity. Based on what you are saying, it appaears that these two crowns would be the only metal restorations left in your mouth (please correct me if that is not the case). I would not replace the crowns simply because they carry electrical current, as all metals do. The biggest problems I see with metal conductivity are when two or more different metals are present in the same oral cavity. However, if your crowns are not sealing properly, and the metal is a non-precious one I would be concerned. Another good reason for replacing restorations would be if your bio-compatibility testing shows reactivity to nickel or any of the other metals used inside these crowns.
I hope I addressed your concern, but feel free to write again if I did not.