Here is a little hoof hack I have been using for a few years now.
Usually when I see poor hoof wall quality I encourage clients to balance the horse's diet. It not ony helps with hoof quality, but coat quality, immune function, performance, etc. But if I can't convince them, I have been experimenting with various topical applications on their horses hooves that can help with improving hoof wall quality.
I have found coconut oil and eucalypt or tea tree oils to be quite effective if used consistently over time on sand cracks.
I had been blending my own hoof oil mixes, but then one day I was in the supermarket and I saw Vicks, and I thought 'hang on, someone is making this already'. The homebrand version is only a couple of bucks.
Here is a hoof wall where the diet has not changed, but I have been applying Vicks and coconut oil in a spray can, both of which I bought just in my grocery shop.
I still feel that diet is crucial, but you can supplement that with topical applications very cheaply to improve hoof wall quality.