Free to see all the visiting classics(or it was last year) and to walk the remains of the track. You can also pay to visit the museum which is well worth the cost.
I did go past the Fiat 500's but didn't stop at them.
Brooklands has an Italian day which used to be very good but in recent years seems to consist mainly of Fiat 500's so I don't bother going anymore, shame as it is only 5 miles from me.