I have a couple of Garmin auto GPS units, 5 to 7 years old, which work fair, I guess. Question: with the latest map updates for North America, are these units just as good as the new units with all the bells and whistles for navigating? Or are the newer units able to guide to destinations more efficiently somehow? In other words, why get a new, expensive unit if the maps, guidance, etc is the same for the older and new devices? Just curious. Thanks. (Note: my current unit is the NUVI 2555 LMT)