There is an unexamined premise in both Nehamas's book and your remarks: that Socrates was a paragon of virtue. Certainly he was fortunate in his biographer. Plato's description of his trial and death is moving stuff. But if Plato was Socrates's Arthur Schlesinger, allow me to be his Kitty Kelley. Why did Socrates wander about Athens "in his one tunic," as you say? It was not as if he was impoverished--he simply refused to work. Thanks to an inheritance he received from his father, he was able to beguile his days by demonstrating to the Athenians how foolish they were. Not that he wasn't good company. Much sought after by the wealthy as a dinner guest, he would stay up chatting till dawn, drinking everyone else under the table and enjoying the services of heterae, as courtesans were called. No wonder his wife Xanthippe had the reputation of being shrewish. And it is by no means true that all the Athenians regarded Socrates as noble. Aristophanes, in The Clouds, makes him the butt of jokes.
Even the Platonic Socrates--the literary creation rather than the actual man--has some grave defects. He is, as Bertrand Russell observed,
dishonest and sophistical in argument, and in his private thinking he uses intellect to prove conclusions that are to him agreeable, rather than in a disinterested search for knowledge. There is something smug and unctuous about him, which reminds one of a bad type of cleric. His courage in the face of death would have been more remarkable if he had not believed that he was going to enjoy eternal bliss in the company of the gods. Unlike some of his predecessors, he was not scientific in his thinking, but was determined to prove the universe agreeable to his ethical standards. This is treachery to the truth, and the worst of philosophical sins.
Socrates surrounded himself with a band of clever, attractive, bad young men, some of whom ended among the Thirty Tyrants who destroyed Athenian democracy. Let's see.a carousing Greek moralizer who hangs out with fascists ... Sounds more like Taki than Ghandi!
Then there is the vexed matter of Socratic irony. I have never liked irony. If I were pope, I would put it on the Index of Forbidden Tropes. I believe in the importance of being earnest. Now, in its simplest form, irony is just saying the opposite of what you mean, while hoping that the cleverer elements of your audience will catch the real drift and feel superior along with you. Socrates professed not to know what virtue was. If irony was his game, then shouldn't we conclude that he really did know the nature of virtue, but was pretending not to so that he could devote himself to tearing apart the theories of his dunderheaded interlocutors? Thus the "paradox" remarked by you and Nehamas--that Socrates led the virtuous life without knowing what it was--gets inverted: Socrates believed he knew what virtue was, but he was not especially virtuous himself. Any way you cut it, it seems, knowledge ain't virtue.
I know, from reading Nehamas on Socrates, that matters are not so straightforward, that irony is a maddeningly complex thing, a wilderness of a million mirrors: Ciceronian irony, romantic irony, dramatic irony, the irony of fate, infinitized irony, irony as trope, a figure, a permanent parabasis ... Most people think of irony as a device that allows the elite to enjoy the same things the masses do--ABBA, The Brady Bunch--while pretending to disdain them. But in the world of learning, irony becomes transformed into something morbid and unintelligible--"infinite absolute negativity," in Kierkegard and Hegel's round phrase. Is such a nebulous and protean concept really an aid to understanding? Or is it just the pretext for a lot of scholarly noodling?
But back to the main question: What, if anything, can philosophy tell us about the art of living? Nehamas says that idiosyncrasy and originality are the sole marks of the good life. You rightly observe that this in nonsense: There are some features that all good lives share. (I hope irony is not one of them.) "Be original!" is indeed a bland and unhelpful injunction. But are there any injunctions that escape these charges? (I have always liked the ring of "Burn with a hard, gem-like flame!") And are they the providence of philosophy, or have we entered the treacherous territory of self-help?
P.S. Professor McGinn, did you by any chance play bass guitar in that '60s rock group, the Mysterians?