It's certainly worth looking at things from a slightly different angle sometimes, and I agree that having a bit of a break can work wonders ;)
My dog retrieved beautifully to hand when a small pup, only for me to spoil it by teaching her to "Drop"!!!

Needless to say i had to have a bit of a rethink and now she understands "Hold" - in fact that is my dumbbell retrieve command now.
I had a related problem last Autumn in doing a search square for working trials, she had just lost enthusiasm. She went in for one article, then lost interest.
So i didnt' do a formal search square for several months, but DID take her toy or toys out into grassy areas and just chucked them in and asked her "Where is it?" She loved this game and now has transferred this to the search square and is getting very keen. I also play tuggy if it is possible with the articles she brings back to add more fun into it.
I feel that if a dog associates the exercise with enjoyment, whether tripe sticks (yum!) or play, then most breeds will do most things :)