Oddly enough, I don't really need it for directions so much as I need it for travel time estimates and travel time and route data review after a trip is completed.
I do this now by running my laptop computer with a GPS receiver that simply writes my speed and location to a text file every second as I travel. This has gotten to be a pain in the rear, and more importantly I'm running out of power ports in my truck. I need one for my computer and one for running the GPS unit, and if I have my roof light hooked up I don't have a spare port for charging my cell phone. LOL.
Looks like you need more than a low end Nuvi. You probably need to look at units up in the 650 or higher model range to get the features you need. Do not assume that any GPS with a USB port will seamlessly swap data with your pc. With Garmin products you need to thoroughly research features and software interoperability. Garmin is notoriously stingy and you pay dearly for anything over basic functionality.