nix on solid laminate deck
Imco small areas like under stanchion bases that have gone bad would be great to cut open and filled with frp. Would be easier as the core transitions to solid laminate near the toe rail.
A whole deck repaired with a 1/2" thick buildup (approximate thickness of the balsa core) of frp would end up adding much too much weight to the boat. Replacing balsa with pvc foam is probably the way to go when recoring as it is arguably easier than building up layer after layer of fabric and plastic. Easier to sand and shape than the grinding on solid frp you'd probably end up doing. When recoring with foam you can use prefered epoxy rather than polyester which you may have to choose because of the many gallons you'd need.
338 had the core replaced with solid glass under the mast. But this area is only a couple square feet.
Composite decks are extremely strong and stiff for their weight, stronger and stiffer than solid, even more so in our case with the strong camber the Ariel foredeck has.
There isn't anything mysterious about using foam in doing a recore. What's mysterious is why it's so damn expensive. Less expensive endgrain balsa is still available.
Imco if balsa is protected (as it should have been by the manufacturer) it'll last forever. There are Ariels that after 40 years have not needed their decks repaired. Balsa is just fine for a whole deck recore that could last another 4 decades.