Yes, Amazon's purchase of the Washington Post will be good for the future of the paper, because Amazon has a history of modern success and it is a strong company. The Washington Post can benefit form the resources that Amazon can provide, as traditional newspapers struggle to stay alive in modern media times.
I mean this is the greatest thing to happens to Washington post, simply because Amazon being lot more bigger company then Washington post. If we think about it from corporate side, Amazon has lot more talent and lot more grounds then the Washington post. I think Amazon's name would drive readers to read the paper and other services they provide.