Hi 'Skyeman'
"Is the Ythan Estuary worth fishing?" ....... Yes, of course, everywhere is worth fishing.
Are you likely to get replies saying what a great place it is to fish? ...... Very unlikely on the forum, for all the same reasons that members explained to you in the Grayling thread.
There used to be boats available from the estate with a ghillie, I'm not sure what the current situation is, bank fishing is also available.
Best wishes
Mike