The officer's assertion was that he was driving 55 in a 35.
He can assert all he wants, but unless this is a citation from the CHP the vehicle likely does not have speedometer calibration records and the officer likely does not have specific training regarding pacing. It would be very easy for the officer to indicate the wrong speed, especially if determined over s short distance. The OP should investigate and learn what is accepted as normal/standard procedure for pacing a vehicle to compare with the officer's testimony. Also find out if the department has a specific policy regarding the procedure.
This is above the prima facie speed by quite a bit and even with the lights on, road clear and dry, it would be hard to beat.
Not necessarily as it does not exceed the maximum speed limit. Reviewing traffic surveys may find an out of date survey for that prima facie limit.
Zig is right, doing 20 over with the lights off isn't safe or prudent
This does not mean the area was not well lit. It would behoove the OP to obtain photos of the area showing the lighting conditions at the same time of day of it is in fact a well lit area.
and the driver was obviously not paying attention to conditions as he failed to detect the police officer until after the stop was instigated.
Not necessarily true. The officer may have come from a concealed area and quickly initiated the stop for the headlights, and before matching speeds and properly pacing. A subpoena for dashcam video, if available (it likely is in that area) will reveal exactly what the officer did, the speed he traveled to close distance on the car (possibly 55), and how long he paced after matching speeds, if at all.
but all that will LOSE at trial because the officer as an expert witness will testify that he paced you at 55, and there's nothing you've said that's compelling that this is in error.
Not necessarily true. While the justifications given so far would not help much, exposing the officer's possible lack of training and possible lack of maintenance records could disqualify him as an expert regarding pacing.
You want something more, it will take an attorney
Not necessarily true. Traffic court is informal and a well prepared person can do just fine sending out a subpoena and questioning the officer on their own, although an attorney would make it easier.
It may all ultimately be for nothing, but there are valid points to raise and questions to ask regarding this scenario that could lead to a dismissal of the citation.