I don't have additional ideas, but I can shoot a hole in a couple that you listed if you will allow...
Chemicals to control the algae could do just that, but the silt will still be there and IMO the silt is still "yucky".
Using a backhoe to clean out the silt will only be temporary as the surrounding silt will soon slump into the fresh hole you've had dug so it's temporary at best.
I'd do like the idea of extending the dock out to deeper water.
