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the building main AC earth ground doesn't meet code. 
The point is that our amp chassis should connect back to the power company "neutral", so stray power current through chassis will flow well enough to pop a fuse. This only relies on chassis-wire and wire-wire connections. Ideally these will all be <0.1r. But at least 6 connections from amp to meter-box. Any one screw-up makes bad bonding.
Whether that power company neutral really connects to dirt is another issue. As you say, it is usually a poor connection, >25 Ohms. Note that 125V in 25r is 5 Amps which will NOT pop your cellar fusebox! The reasons for dirt-bonding are many and complex. GOOD dirt-bonds are (as you know) expensive. The present practice seems to be "mostly OK" based on a century of experience. We do have troubles. It is not clear that more (or less!) dirt-bonding would be better.
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seldom pass the NEC 250.53 second electrode requirement of 25 ohms or less.I tested one rod and got numbers like 60 to 120 Ohms, in a damp month. I have 5(!) similar rods parallel. So I barely have <25r in a damp month. At the moment we are in drought and I can imagine these rods in dry sand over rock are hundreds of Ohms combined.
Note that the resistance of the body can be 1,000-100,000+ Ohms depending on sweat/wet and path. So a >25r or even 500r rod resistance is probably "low" compared to you.
If we imagine the Extremes: if the dirt were good glass, dirt-rod resistance would be infinite however you could not get a shock and would not have large current in a lightning-stroke. If the dirt were metal, we'd have near-Zero rod resistance and near-Zero induced voltage for any current. But all real installations are in-between, with many variations of rods, exposure, and victims, so it is real hard to find any all-around optimum.
