Unless you were going to be using your boat near or in salt water I wouldnt worry about it. The real advantage to Marine wiring and marine connections is that the wiring is Tin coated and the connections are Epoxy sealed.

As long as your wiring is safely ran (Away from heat and moving parts), dont sweat it.

I wouldn't worry about it.  Use standard wire and you'll be safe.  A cheap alternative if you really want the "marine" type wire without paying an arm and leg is low voltage wire you can get at Home Deport for patio lights.  It's usually 14gauge.  Toss some heat shrink on the ends and you should be good to go!