I have looked at the new 590, but not looked in depth as I have a new BMW Navigator V. The Nav V is also new and has most of the technology of the 590. There are some differences but not a lot. The Nav V has twice the internal memory of the Nav IV / 660 / 665. This means there is more than sufficient room for the entire North America map set with plenty left for the always bigger updated maps. They have a faster processor which means they route faster then the 660. They do have BT only for the stereo audio out. I did not like this at first, but as this seems to be the way things are heading with Garmin, I got the BT module for my Autocom. I am very please with the performance and sound quality. No issues whatsoever as the Autocom BT module is bike powered and pairs without issue every time I start the bike. The screen is also a higher definition screen so the detail is much better.
As far as the weather and traffic, the Nav V and the very similar Zumo 590 now use a smart phone app. There is is ONE Time fee for each...approx. $5 for the weather app, and approx $15 for the traffic app....one time fee, not monthly. As long as your smartphone is paired with the gps, it works. There are other features on these new units that the 660 doesn't have and that is the reason I waited for Garmin to release new units...the 660/665 was getting pretty old tech when my 550 died..for the second time.
We all have different priorities and budgets to work within, but if you are already considering a 660/665, I would really suggest you spend a bit more and get the much newer technology of either the Zumo 590 or the BMW Navigator V. Btw, the Nav. v still has buttons on the cradle mount like the hard buttons on the 550 so you have the option of buttons or touch screen.
Cross Country BMW in Metechun, NJ has been running a great discount deal on the Nav.V. Over $100 off for the unit with the cradle. Then spend a couple bucks for the BMW power connector to use to connect the power and ground.