For Bostonians, getting to hear a live performance of Wagner’s ambitious third opera, Rienzi, der Letzte der Tribunen (“Rienzi, the Last of the Tribunes”) was surely a once in a lifetime experience, which is what Odyssey Opera, Boston’s newest opera company, must surely have been counting on. Too bad that even in Wagner’s bicentennial year, and for the landmark inauguration of a new company, only some 600 of Jordan Hall’s 1013 seats were filled (the top ticket price was $200) for Rienzi’s Boston premiere, in a complete concert version. But those present certainly got their money’s worth (and probably so did the local restaurants, which filled up during the two-hour dinner break in between the two parts of the five-hour opera).