The cabin sole on my boat is in really poor condition and needs "rejuvenation". The pic shows the condition so I'm thinking to try and remove the existing varnish and redo it. Has some done this successfully? Any tips?

It's pretty simple but time consuming. Did mine in sections and most sections removed off boat for entire process. Random orbital sander using 80 grit down to 400 for finish. Then 2 pack clear over the top and reinstalled after a few days in warm weather curing.

Go easy with the sanding. The veneers are very thin and easily sanded through

I think I would try one of the gel type strippers to remove the existing finish and follow with a light sanding then refinish.

I did the same for my old boat. I used a heat gun and it peeled off brilliantly.
be warned not to heat one area too much as you might bow the board. Mine only laid flat no screws. So I did a patch here and scrape, patch there and scrap, patch in another spot and scrape.
mine were ply with vaneers

I would use a pull scraper and remove the varnish. Use one of the clear flooring finishes. I like this one.
www.bunnings.com.au/cabot-s-1l-cabothane-clear-satin-cfp-floor-polyurethane_p1521362

No expert (although I do own a cabinet factory) but as per Saltiest1, sand and re coat.

Not sure about stripper at all. Surely its not required in this case as the clear is in good nick just scratched to hell. ie. its sound, not flaking off.

Start with 120 or preferably 150 and finish with either 320 or 400. If you start with 150 and get it back flat, then step straight to 320.

Go easy on the sanding, timber veneer is generally 0.6mm thick (thin).

Like I say, no expert and if you saw the state of my cabin sole you would tell me to shut the hell up...

Thanks everyone- will try sanding a small section and see how it goes