I do appreciate your question, but how many times will people attempt to define art? You are more likely to reach a conclusion by reciting Zen Koans and speaking in tongues.
The problem I had your question is where you suggest that "with enough imagination, just about anything can be justified as art and interpreted to symbolize something". There are really two premises in this statement. The first is that art ought to be justified - or that some things are not art and some things are. This is like saying of any experience or observation - that you need to imagination to justify that it is a manifestation of truth - all things that are experienced are manifestations of reality. There is no "is" or "isn't" where observation and experience is concerned - other than what is determined by your arbitrary criteria (the burden of proof is not on me to prove this statement otherwise as I am only stating that categorizations do not prove or disprove observations other than what is determined by the criteria itself). In simpler terms - lets say that the art Gods agree with your criteria... so what? Things still are. Be a transparent observer.
The other premise in this statement is that art must "symbolize" something. This, similar to your listed criteria, implies an intention rather than spontaneity. As that which is unintended or spontaneous cannot symbolize anything (for example, acts of nature are not symbolic).
Regarding your listed criteria, it seems that both of your criteria are based upon this same premise that art must be intended.
Correct me if I am wrong, but the key description in your first criteria, "expression" implies a communication or atleast a self-reflection of an idea, feeling, experience, value, etc. Under this definition of "expression", an intention must be required. Unless you are talking about a more abstract "expression" like the expression of nature, the universe, God, etc.
In your second criteria you suggest that art can only be concerned with certain subject matter. If this is the case then it would seem that an inspired artist must consciously shape their inspiration to fit whatever subject matter that the art Gods have determined appropriate. This again implies a certain intention on the part of the artist.
To me, it is extremely limiting to hold that art is determined by that which is intended. You are excluding improvised art, conceptual art, art that deals with the abject, religious ritual/art, performance art, and nature (there are infinitely more forms of art, born and unborn, that are not intended that you must exclude under this definition).
Again, what good does it do you to define art? People define art in a way that excludes the Holy Virgin Mary by Chris Ofili or the infamous Piss Christ or other postmodern art from their experience/observation, but so what? It is still observed or atleast has the potential to be! - Regardless of what value you place on it. This is not to say that value is necessarily arbitrary, but it is to say that experience and observations in art are possible outside of value (you must agree that truth exists outside of value/preference) - therefore choosing what to observe based upon value is limiting (although some limitations are of course preferential - this does not imply that art is unconcerned with them).
Oh dear God, I have made the same mistake as you...