My sister in law lives about 30min drive from the bottom of that ride & we visit for a fortnight every year.
I mostly ride on my own over there (makes the mountain lion thing so much more exciting 😯 ) but I’ve never seen so few others at San Juan, midweek or not. Be careful if you ever do go back, on weekends quite a lot of people do shuttle runs between bottom car park & the campsite up top and then only ride down on their biggish bikes. They tend to wait for the “up” people to reach the cocktail rocks but from about 10am they’ll happily fly down it, armoured up – and it can be pretty narrow as you’ve probably seen.
have you seen these already?:
geoladders
Socaltrailriders