I am writing this for anyone with the same problem that is as frustrated as I was. The punch line is that the problem has been FIXED, and it ended up being fairly simple. No bad ABS sensor(s), no bad wiring, no bad ABS module. . .
I learned something about OBD2 readers. The codes they detect can be very, very generalized, and still leave you with many suspect things to check. The P0500 code and its explanation, " VEHICLE SPEED SENSOR "A" CIRCUIT" actually lead me down the wrong path. My Blue Driver OBD2 eventually did produce a more helpful code, which was "LEFT FRONT WHEEL SPEED SENSOR: SIGNAL INVALID." I switched ABS sensors, left to right, right to left. The code did not change. To me, that meant that all the wiring from the ABS sensor upstream was okay.
While all this is going on, I kept thinking back to the fact that about 6 weeks ago, I replaced both hubs and front wheel bearings? The car had been trouble free since then, which lead me to believe it was nothing caused by that repair. WRONG!
Out of ideas, and without any more sophisticated testing equipment, I admitted defeat and paid the local Ford garage their $100 diagnostic fee, with instructions that I would do the repair. The answer came quickly. The technician reported that both front ABS wheel sensors were giving sporadic readings. He was able to spray brake parts cleaner into the right side sensor and basically clear it up. Not so much with the left one. His advise was to take everything apart and clean it with wire brush and brake parts cleaner, as some of the grit and rust was laying on the surface of the tone ring (the magnetized strip attached to the inside of the wheel bearing that is "read" by the ABD sensor). There is a reason why they say to NOT use any lubricant when pressing in wheel bearings with magnetic tone rings! That lubricant had attracted the grit and rust particles, which interfered with the ability of the sensor to read the imbedded magnets.
So I once again replaced the wheel bearings, this time with Ford parts (made in Japan, not China). The tone rings are pink, which helps you not press them in the wrong way. I put it all back together and just like that, every single code went away.
If I had a professional scanning tool, and could have looked at an oscilloscope graph of each ABS sensor, I could have diagnosed this myself. I have since fixed that problem by purchasing a X-TOOL D7S. Hoping it is the best money I ever spent!