I am very happy report that I just vaporized my crappy Pioneer car stereo in the boat. The thing was a total piece of junk. It frequently overheated, it had about two mouse-farts worth of amplification and the Bluetooth range was 30 cm on a good day. So, destroying it with an interesting wiring mishap is a blessing, as I am now able to start again with a clean slate.
I am looking for a decent stereo head unit, with Bluetooth, Spotify if possible and an iPhone app. I am not all that keen on the marine stuff, it seems terribly overpriced and the interior of my boat is drier than many of the cars I have owned, so it doesn't seem important. I figure people here must also be using car stereos in their boats and might have some recommendations.