Why would the plebs have needed to secede again? By the end of the Punic Wars they had gotten everything that they wanted. They could hold pretty much every magistracy, except for some of the patrician aedileships, and there had been a plebeian consul sitting each year forever. They could sit in the law courts, the tribune of the plebs was extraordinarily powerful, and the increase in wealth throughout the state meant that the equites, plebeians who held enough property to qualify for senatorial enrollment but had no political ambitions and didn't run for any magistracies, were the most rapidly-expanding group in society. The senate was made up almost entirely of plebeians by Caesar's lifetime, and at least half of the nobiles, those with a consular ancestor, were plebeians--by Caesar's lifetime only fourteen patrician families still had surviving lines, out of the fifty-some-odd that we know about from the earlier period. Cicero, Marius, Cato, Pompey, Crassus, Antony, Brutus, Cassius--all these people are plebeians, not patricians. The distinction between patrician and plebeian had long ceased to be meaningfull--a good case could be made that it was by the Punic Wars only a ritual and traditional distinction.