Good advice about going to the beach, seems like a much safer option and hopefully more space available but its still tourist season and the beaches are always packed anywhere in Devon, unless someone knows a quiet one?
Cow debris does sound worse, at least the sheep stuff was dried and easy to brush off.
If your thinking of the 5.5 - go for it, its great - just take care.
I'd still recommend Dartmoor its just restrictive on space as there is so much gorse which you don't want to get either yourself or the kite stuck on. Flying a super 10 from the bottom of a hill was a bit different (it was just above the ground at the top of the hill), and you still get a clear view of anyone approaching.