I agree. I hate to be a party-pooper, but I have not seen a significant degradation of the subway system. In my opinion, the homeless are not the problem, but rather the people who eat their breakfast, lunch, and dinner on the subway as if they are at home, without regard to the senses of the other passengers who may not appreciate the smell of the latest third-world cuisine de jour.
I also think subway etiquette has improved because everyone is on their iphone ignoring other passengers instead of - for good or bad - interacting with each other.