Well it's about time!
Jim, I like your modification idea. Even 1/4" high tensile steel is a bit stretchy. SS is simply not in the same league with HT as far as stretch. The 1/4" SS should be fine underneath to prevent bounce.
I would go with 1/2" HT, and de-grease, prime, and paint it with a good epoxy paint.
It would also help to pre-load your cable until the end of the wharf is lifted up 1/2" to 1".
Another alternative would be to brace it with a box beam, triangulated underneath the structure. Start it somewhere between the end and the ladder, and attach it at the base of the concrete forms. If you could bend the beam into a gentle arch, it would look fantastic.
The cables look super, BTW. Here's what came to mind when you first started your project: cable stays!
