Navigation System Software Updates?

Toyota sells map updates through the dealership. The data in your Nav is updated via the USB port. I haven't seen an update as they're generaly only offered in the fall, but I'd guess the price will be as little as $100 and as much as $199.
Unless you're running into troubles: Missing street data, I wouldn't be in a rush. If you're using Entune and have seen the "Bing," search App. This will give you the most up to date POI data. True, there could be a missing street and that would require a dealer to update.

 

When I bought my Prius C the dealer told me if I connect my smartphone to the EnTune System that when I hit the app for "maps" that the phone supplies the updated google maps to the EnTune System via the phone, and the pre-loaded car maps are turned off, and if you disconnect your phone it will resort back to the pre-loaded maps

So really no need to buy the upgrades, but it seems to pan out I have more details on my smartphone provided maps than on the factory loaded maps

 

That would need some verification. I'm skeptical that Entunes uploads Google maps to the car, that would be a lot of data and lot of discussion between the car's nav computer and the smartphone, two devices that barely talk as it is.

Since Toyota sells the map updates (I was quoted $168 by dealership a couple days ago) it also makes no business sense. The navs on cars are pretty crappy and the updates not worth it.