The number of people watching is not really connected to the money that the sport gets. In fact, I'd say they are probably inversely proportional. Take the UK in isolation, the Sky TV deal brings in a lot more money than the previous BBC or ITV deals, yet has significantly reduced the viewing numbers.
The same is the case for trackside fans. The venues pay their hosting fees, and then recoup that cost by selling tickets. There are queues of places lining up to host a race with government backing where they will happily sell no tickets as the funding for the hosting fee is not connected to the ticket sales.
So at the end of the day, nobody in F1 really cares if we watch or not.