On the Symposium, please see notes on the web: http://www.personal.kent.edu/~jwattles/sympos.htm
In the Symposium translation used in our text, Jowett butchers a key passage on p. 62. Here's a better translation by Alexander Nehamas and Paul Woodruff: "First, if the leader leads aright, he should love one body and beget beautiful ideas there; then he should realize that the beauty of any one body is akin to the beauty of any other and that if he is to pursue beauty of form he'd be very foolish not to think that the beauty of all bodies is one and the same. When he grasps this, he must become a lover of all beautiful bodies, and he must think that this wild gaping after just one body is a small thing and despise it."
In the excerpt from the Symposium in the Ross anthology, Socrates will speak first of the being and nature of Eros, and then of his works (56c). Diotima proved Eros neither beautiful ["fair"] nor good. Intermediate. Neither mortal nor immortal, but one of the spirits [daimon] mediating and communicating and interpreting between mortals and the gods (57b). Originated in Plenty and Poverty (57c).
Eros is desire for the beautiful . . . to possess the beautiful (58c) [one of the ways toward the good and happiness which each desires for himself (59b)], which they can only love if they take it to be good (59c).
Eros is "love of the everlasting possession of the good" (59c).
Eros seeks "birth or procreation in beauty, whether of body or soul" (59d)
Love is of immortality (60b): physical . .
Those who are more pregnant-creative in their souls than in their bodies (61c) bring forth wisdom and virtue, which brings order to states and families; and they devote themselves to the education of young persons.
On the Ion, note the difference between the knowledge for which Homer is reputed and the knowledge Homer lacks. Nor is Ion inspired, despite S's ironic praise, since he shows himself a crafty manipulator of crowds. Nevertheless, the image of inspiration flowing from the muse, to the poet, through the e.g., rhapsode (performer), to the audience is suggestive of an insight in philosophy of mind to which Plato never obviously returns in the dialogues. Note the concept of techne = know-how (a certain knowledge is involved, not merely a knack), also translated craft or art (but not to be confused with poesis, making).
In the Republic, grasp that Socrates' critique (how much of this character's critique is Plato's?) of "mimetic" poetry (mimesis=imitation, in Kant's terms, representation) is that it fails to seek the truth of the things that it copies from the natural world and thus characteristically tends toward simply arousing the lower emotions to gratify the masses and tends toward error in conceiving the character of divinity (God should be perfect, good, wise, beautiful, all knowing) and the grandeur of genuine character achievement (the hero should not be afraid of death, but resolutely courageous). Socrates is continually dropping words that suggest his self image as a poet, but one who seeks the truth (the eternal forms—you may look at the early portion of this: http://www.personal.kent.edu/~jwattles/forms.htm though it was never required nor presented as a handout, but some of the thoughts there were expressed in the lectures). The eternal pattern (the bed in heaven—how marvelous to sleep on! [irony here?]) is deliberately conflated with the eternal form (bedness/the structure of the bed that the carpenter must know (but not the mimetic artist). Then there is the bed that the carpenter makes and the bed represented in painting. Presumably, the Platonic artist would make a point of learning something of what the carpenter knows (if not the techne, at least the blueprint).
Plato's opponents were the sophists, who denied the forms, denied any eternal truth, any transcendent beauty or goodness, and who asserted cultural difference (in today's terms, "Beauty is in the eye of the beholder"=the version Kant criticizes, "Everyone has his own taste") as the last word on the question of standards.
Plato does not teach the aesthetic view that "Beauty is in the eye of the beholder." That view not only makes the point—which all philosophers recognize—that people differ in what they find beautiful. That view also claims that there is no standard beyond individual opinion (anyone's view is as good as anyone else's). Plato holds that there is an eternal form of beauty, "the beautiful itself," which is not a subjective affair of what any person happens to prefer. According to Plato, some are more advanced than others in their realization of beauty. What I did say was that Plato recognizes the grain of truth in that theory when he implicitly acknowledges that people's views differ regarding the beauty of bodies, customs, and so on.
Let me also clarify that Plato never says that everything is beautiful. The beauty in beautiful bodies is akin, he says; but this is not to say that every body is beautiful.
Even the Navaho concept of walking in beauty implies that we humans have a responsibility to restore beauty.