If he is a pasture pet, walks sound & does not appear to have any painful lameness issues, adjusting him is the Big $64 question as to whether or not he will stay in place, and would you be opening up a can of worms by doing that.
Toeing in, with knees out is something that won't be fixed by this time. It is likely going to beget arthritis over time. Cosequin ASU+ (Plus) really does seem to work but it's expensive. If you can see your way financially to starting him on it, you might look at the clinical studies on Nutramax website.
You're doing the best you can do for him:). Except for putting a high caliber chiro on the payroll to match every one or two trim cycles, you're probably doing all that can be done:)
My horse's chiro is supposed to be here every four weeks to work on his fractured sacrum, if he needs it. Bout two months ago, we had a heck of hail storm with quarter-to-walnut size hail. I couldn't get the horses in because the other horse was raising panic h***, running the fence and spinning. My injured& foundered horse followed suit as he is the lower herd horse.
Somehow he managed to seriously re-injure himself --- to where I thought I might lose him. Between the traditional vet/chiro, the hollistic vet/chiro, and the 60 minutes daily therapy instructions they gave me, we managed to put "Humpty Dumpty somewhat back together again". His new normal is now to see the hollistic/vet chiro every two weeks until further notice and I will likely be doing 60 minutes of therapy daily for the rest of his life.
To look at him standing still, nobody would know how injured he is or that his founder nearly cost him his life seven years ago. I honestly could have a decent Dressage horse and two years of lessons to learn to ride dressage for the money I have in this guy (my avatar BTW:)
Meaning, keep doing what you are doing, within your financial means, until the horse tells you he is too tired to try anymore:)
Also, think about the California Trace since you are in California. It is too high in selenium for some of us in other areas of the U.S. :). However, if it is being added along with other products containing selenium, be alert for over feeding (including what is in your hay) as selenium is the one thing that can cause toxicity in horses if fed too much:)