Add a table of variable values, that will represent science, engineering and common knowledge, that race A have about race B, and/or a race variable, that indicates overall xenology knowledge level of this race.
Both levels must have an increase, when your sigint, spies, interrogators, traders, xenologists etc have a success with some race or artifact (the last is a reason for high-tech races to explore low-tech ruins too).
Overall xenology knowledge level have to be a multiplier for the table values increases. Table values have to be multipliers for new sigint, spies and interrogators deals, or even some increase in detection radius and fire accuracy (especially at ground combat).