Like others said before, I do believe it is possible for an individual artist to progress in his art. I also think that there exists objective features of the beautiful (harmony, symmetry, etc.)
That being said, I do not believe that art has to be beautiful. The progression of art, if there is one, seems rather to be towards a questioning of traditional standards of beauty, as well as what we traditionally take to be "representation". Would you say that postmodern art is beautiful? And yet it is undeniable that it has been at the forefront of artistic innovation. I think that art progresses insofar as it manages to capture the spirit of an era, and to question it.