(A guy with two 33 ft boats is concerned about price?
What you're proposing is entirely reasonable; in fact just about avery modern networked marine
system based around a MFD or chartplotter
is essentially just that - a system with one main "handler" and a number of sensors and displays all working together.
I have a couple of Raspberry Pi's - I think they're pretty amazing, and make great platforms for testing and experiments, but I personally would want something more powerful and robust as the main brain of a reliable system for offshore
You also have to think about redundancy and independence in the marine environment
. You don't want to have one point of failure that would completely cripple the boat.
But, yeah, I do think it would be a really interesting project
. I have an old eee running Linux dedicated to boat experiments as well as a host for OpenCPN