You are at the same point that I am with the c80.
Unless you can find a decent used dome, I would find it had to put more money into this obsolete series of devices. Garmin has a very nice series of devices but have not looked into how they would fit into the dash. The issue is most of the newer raymarine units are wide screen but the c80 is a 4:3 screen.
Have you joined the raymarine forum? That seems to be a good resource for c80 questions as well.
Let us know what you decide if you upgrade.
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Jnizi2007 Vista 338 "Better Yet"
Previously:
2007 Vista 258 " Just Right"
2005 Horizon 230