The aircraft making low level calls in the circuit needs to be in range of the VHF outlet and I'd hazard a guess that the number of such circuit calls being made on any frequency is tiny.
No need to guess. You are correct: The number is tiny.
More than a few pilots inadvertently make calls on area rather than CTAF already and it's not a huge problem -
During a recent trip I was surprised by the number of calls made by Centre advising aircraft that the CTAF call had been made on the Area frequency. It seems to be increasing.
I'm more concerned about their calls being missed on CTAF than the effect it has on my traffic.
Me too. That's why 2 VHFs can be helpful (for those of us that don't crave "beautiful silence").