From what I understand, whether or not you need the electronics upgrade has a lot to do with where you live. I believe it costs about $1500. That said, my '76 Series I guitar hasn't had the upgrade. I live in a dense, modern urban area (S.F. Bay Area) and I've had no problems yet with RF interference. I suspect the problem may also be instrument specific too. Some need it, some don't.
Bill, tgo