My cabin sole is teak and holly veneer plywood. (I can see the plywood joint at the nav table / galley sinks.) A previous owner had sanded through the veneer in a couple of places exposing the base lauan plywood. I played artist and painted the veneer back with acrylics. It is not too bad. My advice is to only use a power sander to rough up the existing varnish before adding more coats. If you want to strip the sole, use either chemical strippers or heat. And in both those cases, get some experience on something from the dumpster before you start on the sole. It is just too visible.
Find copies of Rebecca Wittman's books.
I have used Varathane three times to add varnish to the sole without any problem. The best system seems to be to cram the cushions in the vee berth, put plastic sheeting over the settee bases, rough up the sole with an orbital sander, place all the floor plates and floor mounted table on the settee bases, tape off all the fiberglass edges, brush around the edges, roll on the varnish, and tip it with a good brush. Then give it 12 hr, another coat, 12 hr, another coat, then go away for a week or so before putting everything back together and walking on the new varnish.
1988 PSC 34