I say go. It sounds to me like you'd regret not going. You don't want to live your life wondering, "What if?" I think in the worst case scenario, if things don't work out, you can pack up and move back to SD. Or maybe you fall in love with Nashville anyway and stick it out there. I think it sounds like it's worth taking a chance on.
Also, because the cost of living is less in TN than it is in CA, the pay cut that you'll face shouldn't be too bad. It really is so much cheaper to live out this way than it is to live in San Diego.