I tend to think that there is a good size for flat art, like paintings, prints, photographs, etc. You can't say what it is, exactly, except that it should be appropriate for its setting. It shouldn't be too crowded, nor should it look like a fly on the wall. People shouldn't have to put their nose against it to see it, either. So the appropriate size is different for different articles, in different spaces. Small is fine, for the right space. (I have a four-inch square engraving hanging next to a toilet; it's just fine there.)
The problem with photography was that it couldn't be too large and still maintain acceptable resolution. It was sort of arbitrarily small. That's why people were so awed (I believe) by the giant Polaroid prints that were fashionable for a while -- they were so close to perfect that you could see things about faces, for example, that you couldn't see in real life, with the naked eye, or would be embarrassed to look at.
There were ways around the problem, but they were very expensive and not very practical -- using 8x10 or larger negs, with an enlarger the size of an automobile. And what if you wanted to shoot a basketball game...? I believe only a few of the over-sized Polaroid cameras were ever made, for example, and they were sort of shipped from one fine-art photographer to the next, or were set up in one space by Polaroid and then the photographer was invited to come to the camera...
We may now be breaking free of that that problem. Once we get to four-foot prints of acceptable resolution, done with affordable equipment, I think photography will begin to challenge painting for high-end wall space. And people who complain about the cost should realize that high end photography was never cheap. I suspect a professional Hassy kit (body, backs, Polaroid back, a half-dozen lenses) would have pretty much taken all of a typical American family's annual income in 1960. A P22 & a decent Hassy kit would cost just about a typical American family's income in 2006. (But I really haven't looked it up.)