Well, there are some specific bonuses that Machu Picchu gave us. Archaeologically speaking, the existence of an intact Inca settlement (especially a royal estate like MP) has been a windfall for numerous studies of the Inca Empire, often without having to consult the primary sources as strongly.

Astronomically, the Torreón is an incredible astronomical observatory space, with alignments to the summer solstice, the heliacal rise of the Pleiades, and the heliacal rise at sunset of the tail of Scorpio. Each of these had a role in timing the year for the Inca, and controlling the standardized beginning of the calendar year, time for planting crops, and the opening of the storehouses, respectively. Extended archaeoastronomical studies in the valley there have found alignments to several adjacent mountain peaks, which could be viewed form the Intihuatana (the sun-hitching stone, AKA "where the aliens landed" eyeroll). Taken together MP has been an instrumental example of showing how the Inca tied themselves into their sacred landscape, and used to to maintain power over their people.

MP has also been excellent for studying agricultural, architectural, and hydraulic engineering feats of the Inca. We still do not fully understand how well they maintained water flow through the site, for instance; five hundred years of disuse "clogged the pipes", so to speak. Some studies seek to maintain structural integrity of the buildings, which means understanding what is causing weakness in the foundations. At times this is due to poor redirection of the water through the site - something the Inca had figured out when they constructed it.

There are also numerous little bonuses archaeologically: for instance, the only complete set of Inca silverware was recovered in context at MP.

I'm in Cuzco currently, and will be visiting Machu Picchu at the end of the month. I will be able to take some good pictures and update this post. In the meantime I'm plugging away on some ceramics analysis; however if you have more questions I'll be happy to answer them here, over the course of the afternoon!

EDIT: Musing a little more about this (and while I have a free moment), I would add that in a very general sense Machu Picchu is very good at illustrating the layout of an Inca estate. There are a few relatively intact places with Inca layouts (Ollantaytambo comes to mind, also in the Sacred Valley), but most Inca cities were co-opted and built over by the Spaniards. I take it you were in Cuzco during your travels, that's an excellent example of how the Spanish literally built atop the walls of the Inca canchas. Thus having a more "pristine" example like Machu Picchu or Choquequirao is helpful - to understand movement of individuals through the site, points of access, who lived where and when. At MP specifically a whole section of the site was more continuously occupied by retainers of the Sapa Inca (the emperor), who showed up intermittently. The austral winter is pretty chilly here in Cuzco - it's a little more temperate at MP, so the Inca could come and stay for a few weeks when he desired.

Having the archaeological capacity to explore these behaviors and demographics intact is pretty incredible!