Your blue Heeler is cute.

I have a red boy.
So your feed is mostly corn already and about 16% protein? Scratch is often 7-8% and doesn't have any added vitamins/minerals/other nutrients added making it on par with a bag of chips or candy bar, as well I think that's about where corn lies too. Is your spinach fresh or cooked? Your scratch daily and other treats should be not more than 10% of total daily intake. The ladies you mention are both dual purpose breeds and will do better with a little more protein (supporting link to follow). Studies have also shown better hatch rates and chick vitality when the parent stock were fed a "higher" protein diet (that means a few % not extreme anything beyond 28 would be considered detrimental to chickens), which to me says better nutrition in the eggs my family is eating. 16% is the minimum for light bodied layers like leg horn. And feathers are made of 90% protein and the amino acids it contains. This is one reason why many who show their birds feed higher protein, they claim fuller/shinier feathers. If protein is diminished beyond that 16% it could cause all kinds of issues like delayed or decreases production, feather eating and even cannibalism to name a few. I would skip the extra corn altogether, though I do like to let them peck at the cobs after we've enjoyed them. The link has one misprint that says 5-17% and should say 15-17...
http://ucanr.edu/sites/poultry/files/186894.pdf
With anything posted on here, you gotta do what YOU think is right and what makes sense for YOU. This is my opinion based on my research, experiences, and perspective. I feed 20% flock raiser with oyster shell on the side and access to good pasture (meaning a variety of plants and bugs). All of my birds are dual purpose. Plus I have chicks, layers, molters, broody's, rooster and some of them don't need the extra calcium inside layer and it's easier to feed the whole flock one feed.
How many roosts in the coop? How far apart are they? Is your yard gonna stay green through winter?
Some high protein treats are meal worms, scrambled egg, any cooked chicken/beef/turkey/peas/beans... that kind of stuff. Chicken are omnivores.

And I always set aside their shells and let them dry to avoid mold then crush a little and feed back in a separate dish. They really like it, saves you a little and it and in NO way does it cause egg eaters.