I have owned GPS's for a while: GPS 45 (one of Garmin's first), GPS III, GPS V, Zumo 450 and Zumo 550. What they all had in common was the screen was too small. Even the new Zumo's are 5". At $250, for the unit, FJR spindle mount and cradle, the price was definitely right. That's with lifetime maps and traffic. With Bluetooth and voice commands, you can control it with Cardo and Sena communicators. I'm deciding which communicator to get so now I just test the unit in the car. I know the Zumo 550 doesn't come close to the performance of features on this Nuvi. It really needs a BT comm system to make the features work like that of Zumo, but if you have it then the rain issue "ain't no big deal." You can navigate by waypoints or route in the rain by giving it voice commands and listening to the directions.
P.S. - I did not have plans to get a new GPS because there aren't too many places from OH/PA down the Appalachians to N.Ga I haven't ridden (KY is an exception which I intend to rectify this summer). The GPS's I've owned were NOT a necessity by a long shot. That's what made cost a significant factor in my decision.