I can't speak to the Galapagos Islands, but I can tell you that Machu Picchu is quite a bit more dramatic and impressive than the other Inca sites in the Sacred Valley. Several of the other sites are worthy of a detour because they are easily accessible during the journey from Cuzco to Aguas Calientes (the village at the base of Machu Picchu), but in no sense should they be viewed as acceptable less crowded substitutes for Machu Picchu. It would be a waste to travel all the way to Cuzco, Peru, and NOT to go to see Machu Picchu. Yes, it can get crowded - but the crowds do not diminish the significance of such an elaborate ruin (an entire town, in essence) that has been built atop such a remote and steep mountain.