How long do you intend to keep the boat? From the factory, these decks were typically unsealed and lasted many years. Not sure how many coats of Spar you have on there now, but the vinyl should also prevent/minimize any water exposure to the wood once you have it put down. I personally would just proceed with the vinyl, but I also don't know how much exposure it's had since the spar was applied. I also don't know how you intend to store the boat moving forward, so that might play a role in your decision making. Mine sits in a climate controlled garage and covered anytime it sits outside, so any exposure it sees from routine use won't be enough to deteriorate the decking in my lifetime, and I didn't build it with intentions of it lasting for another generation past mine, whether it does or does not.
I would revisit your storage methods and see if there is a better way to prevent water intrusion or moisture build up moving forward. Maybe a better cover, different tarp, or just some other adjustments to mitigate what exposure you can.
