Arklier,

It's not so much the size of the boat as it is the stability of the boat that matters. I used to fish my 14' driftboat 3 miles out at Seiku for silvers with my kids but you couldn't pay me to step foot in the old Sears Gamefisher lightweight aluminum boat I spent my life in as a youngster on the Sound. Worse case scenario, if I lose power or get caught in a storm, I want to be able to hunker down and drift till they find me, as opposed to being flipped over and counting the minutes I have left on this earth, PFD on or not. Its not that you need to go far or fast for salmon in the sound but you do want to be able to ride out an unexpected storm if you had to.
Also, fishing in a small craft with higher gunnels and less rocker is definately preferable. Good news is there are many good designs in small boats for the sound, The tried and true craft for Sound waters is the "kicker". The shorter "Livingston style" (twin hull) boats have proven themselves also. I prefer the fiberglass boats in the salt but Lund and Valco are worthy aluminum boats too.