Is that people will be not nice, or nice depending on how they percieve you. If you have gotten older, more frail (less of a threat), and smile first, i think that it would be an "i think people are getting nicer" call. I say this because Americans, and people in general, live by codes, where they tend to respect their elders, and have compassion to those with disabilities.
If you appear young, poorly dressed (i mean unwashed, and in tatters; not a suit and tie that doesn't match! ), and present with a smug, cocky, threatening attitude (the eyes are the window to the world), people will react different to you, and you may percieve them to be "mean"
I also think that there is a thing about being in pain or sorrow. People see it on your face and the "instantaneous mental skake down" that they get is that you are more conncerned with your own matters and as such, prove less of a threat to them. AS an example, people inn your way in the grocery store. They know that they are impeding you, but you just wait patiently for them. They are playing a little game, trying to force you to be rude to them so that they can do what they do best, hassle with you. But if they see that you are trying to hold youself up, they see your cane, and an unperturbed look of serene patience on your face, they more often than not apologize and get out of your way. This example can have hundreds of similarities to it.
I do think that because of a faster paced life, and the increased pressure to make a buck, people are less patient than they used to be, but "meaner", not really. cs