First off, I have a 2013, and it's my daily driver.
I use a ram aqua mount with a nuvi... 2557 and have had no issues so far. Its only been on the bike for only 700 miles so far tho (rain included). Completely waterproof (including the cable hole in the back when siliconed), has a lock hole and I lock it to a cable I made that goes around the bar riser. The touch-screen is resistive, so it works with gloves, and with the aquabox flexi-screen thing.
Inside the case its supported by foam behind it which I carved out for the power cord, and I also added supplementary pieces of foam around the border of the unit. Wired a 12V socker under the seat to the key-hot accessory wires and so when I turn o the ignition, the GPS turns on. When I turn it off, the GPS detects that and shuts off. The foam I think greatly helps with the vibrations.
I dont feel the need to have audio as I also read speed limit data off the unit so I check it often. I also pay attention when I know I am reading directions from it.
Would a dedicated motorcycle one be nice? Sure. But when it comes to electronics, vibrations are vibrations. The best way to eliviate that is to reduce the viberaitons that get to the housing. Period. The foam in the aqua box is good for that. Plus, $200 (mount included) is a lot cheaper than $600!
I apologize for any typos... On my phone. (Not-pictured, my lock cable. Hadn't made it yet when the pix were taken.)