Do you mean patricians? Because senatorial elite and senators in general were not become less relevant during the republic, as a roman became a senator after he took the office of a quaestor, the first position in the line of roman public service offices. And it wasn't limited to patricians only, for the most important offices there were no restrictions for plebeians, though there were some special positions for patricians only and for plebeians only. Examples - Cicero was a plebeian, even a novus homo (a politician without senators among his ancestors); Cato the Younger, one of the leaders of the optimates (traditionalist fraction in the senate), was a plebeian, though a member of plebeian aristicracy, descendant of Cato the Censor.

Edit: i think i misread your comment, so there is no arguing with you actually.