The perspective from a CHP officer's point of view:
If he stops someone and decides to give them a break (writing them for "70+" instead of 80, and then they try to beat it in court, here's what happens.
First, the officer gets overtime for the hours he's in court, so please please please take it to court. Please.
Second, when it's his turn to testify, he gives info on his training, his equipment, the situation, and what he saw. Typically, he will indicate that to give the speeder every benefit of the doubt, he wrote the ticket somewhat lower than his professional judgement indicated that the speeder was going at.
The judge usually asks the speeder if he was exceeding the speed limit. Regardless of the actual speed, if there is any indication that the person was going any amount over the speed limit, the ticket is upheld. If the accused refuses to answer, the traffic officer's professional judgement is taken as the only real testimony given.
The CHP officer I know is retired now, and he doesn't recall losing any trips to court over speeding tickets.
That said, it usually doesn't hurt to go to court because if the officer fails to show up for whatever reason (illness, duty, etc), the ticket is often thrown out entirely. If the officer shows, you tell the judge that you're there to discuss ways to get the ticket off your record in the shortest time and that is usually a fine, traffic school, and you're record is clear somewhat sooner than otherwise.
But trying to actually beat a generous ticket... You might end up irritating the judge and at least in California it's unlikely you'd get the ticket thrown out if the officer has any amount of competence in giving his testimony.
