Someone will know this better than me but I think different elite courses have different policies:
I seem to recall TOC is the most with close to 60,000 rounds, fourballs dawn to dusk every day of the year bar Sundays.
But some of the elite courses limit visitor play to an extent so can be a little empty at times. Nothing like some of the more exclusive American courses I expect. You are probably right that 30,000 is about a norm.
In Ireland, Ballybunion and Lahinch are packed out, Portmarnock restricts visitors a bit more and a place like Carne was only seeing about 11,000 rounds even when visitors were at peak. Contrasting that, Strandhill was getting closer to 40,000 because of the large, vibrant membership.