I just bought the Garmin GPSmap 76 for my new boat and am impressed with the quality of its construction and ease of use.
In retrospect I dont think Ill use the ability to upload charts very much. I interfaced the unit to a laptop and get the graphics that way.
I had a garmin unit on my old boat. I bought it in 1994 and would not have replaced it if I still owned that boat. You are right in assuming that the latitude and longitude are the things you really need it for. The rest of the features are fun to play with but not really that essential.
One thing about the 76 is that it comes with limited street maps built in and you can download street maps if you want to use it in your car. You can change the units to statute miles. Mine seems to have no problem finding enough sattelites through the closed sun roof of my car. It is not as sophisticated as the car navigational GPS units but itmight be handy on a long trip.