Solatar,
Well, regarding your views on the matter, it seems to me that I'm relatively inclined to both perspectives you raised on the issue. The biggest problem in your extreme relativism (art is 100% in the eyes of the beholder) is that then the very word "art" loses meaning in a conversation, since the very idea of a "word" is to share between sentient people the same experience (of an object, of an event, of a pattern, etc.). If "Art" is entirely subjective then it isn't "shareable" at all. If, however, we can share anything we experience as "art" with other sentient beings and feel we are talking on "the same page", then the experience is shareable.
And it evidently is, historically speaking, since so many humans have expressed and shared so much of it and so much conversation about it. So even if people harshly disagree if X is art or not, the very word "art" clearly expresses a concept that both (at least vaguely) share. So in here, we have a falsification of your idea.
OTOH, art is definitely not as objective as any science. The very thought of it being so is ridiculously funny, and every attempt to constraint art into a "set" of stuff one makes with a "set" of tools, a "set" of process, with a "set" of purposes turns art into decoration, or worse, into a product. So of course that in this view, I am deeply inclined to your subjective stance that the art is "in the eyes of the beholder".
I also understand the notion that you can produce your own meaning while watching a piece of art, unrelated with the author's intent, althout I find that phenomena more secondary and serendipitious. The difference is however that a more comprehensive experience and knowledge one has of the historical context, the stories and the meanings that surrounded each piece of art when it was done is undeniably correlated with a much better enjoyment of each and every piece of art there is out there.