I had never tried tourism victory before, so I went ahead and experimented a little. I tried Parthenon just because it was part of the show. To me I think it would be stupid to rush it. But on the harder difficulties, does it anyone find it essential for tourism victory? One of the main flaws I see in it, is that by the time you build it you might not have met all the civs yet, so that early tourism would not help at all for becoming influential to civs on other continents.