Example 1 comes from Hugo Wolf's Spanisches Liederbuch—the eighth of the Geistliche Lieder, "Ach, wie lang die Seele schlummert!" The opening section is one of Wolf's typically obsessive, austere, serpentine bits of chromatic counterpoint. But when we get to these words—
Doch nun ihrer Sehnsucht Licht—the harmonies become suddenly opulent:
Blendend ihr in's Auge bricht:
Zeit ist's, daß sie sich ermuntre.
But now the light of longing
Shines blindingly into [the soul's] eyes:
It is time for it to wake.
That ii7-V9 color sure sounds familiar, doesn't it? It's almost the same harmonies Puccini later used for the "Te deum" finale to Act I of Tosca:
Now, the question is whether Puccini stole from Wolf, or whether both composers were paying homage to a common source—or both. The Spanisches Liederbuch was published in 1890; Tosca appeared in 1900. (Mosco Carner, in his Puccini biography, mentions that the "Te deum" was partially recycled from an unpublished 1880 church anthem, but no other source sees fit to mention this, so I'm guessing that, if Puccini was stealing from himself, he changed the source material quite a bit along the way.) A search through the published letters and biographies shows no mention of "Ach, wie lang," but I can't imagine that Puccini—a composer ever keen on staying abreast of every latest musical development—didn't know at least some of Wolf's music, so it's at least plausible that Puccini had Wolf's refrain in the back of his mind. It certainly fits the point in the opera—Scarpia is exulting that his best-laid plans are now on the verge of snaring Tosca for him; his pitch-black soul is, at last, fully awake.
More likely, though, that both composers were borrowing from the inescapable Richard Wagner—to my ear, one of his bridal processions, possibly Lohengrin, but more probably Götterdämmerung:
Wagner settles this motive into a V7-I pattern which then embarks on familiar Wagnerian chromatic excursions. But Puccini and Wolf translate the harmonies into a static loop where tonic is delayed. It's far closer to the language of Tristan—or, in a way, the epic E-flat-major triad that opens Das Rheingold (which, when it finally does move, goes to the not to the dominant but the subdominant—where Wolf and Puccini start). Wolf and Puccini are stealing one of Wagner's most reliable dramatic conceptions—the stately tread of ceremony as a backdrop for a tightening or release of emotion—and, seemingly, conflating it with some of Wagner's most radical harmonic experiments.
In other words, they're not just stealing something because it works, but because it also signals—to listeners, performers, or maybe even just to themselves—that they, too, are on the cutting edge. It's a claim of modernity. Interestingly, a lot of musical quotation/borrowing/pilfering today seems to go in the opposite direction—composers borrow to assert continuity with the past, with tradition, with a long-standing musical vernacular. Maybe it's a gesture of reassurance—either to the audience, that the music is not aiming for the shock of the new at any cost, or to themselves, that they can reconstitute the narrative of cultural success and prominence of the great composers of the past: a claim of canonicity. Choose your causality: the preponderance of conservative programming, the recorded ubiquity of the entirety of musical history, the more forbidding nature of recent modernism. (My biases: maybe, yes, probably not.) But it does make for an odd state of temporal affairs—the idea that being up-to-date is less up-to-date than it was a hundred years ago.
Update (4/11): I coincidentally ran across a pleasantly loopy echo of that last idea today, a blurb on the cover of a 1995 sci-fi novel called Strange Attractors: "A 2001 for the nineties."