I had to replace about 40% of the balsa core on my boats foredeck and roughly 30% of the core on the cabin top. You are correct in that it was a difficult and time consuming job, but it's one that I see no way around. The main problem I see with the quick-fix solutions you propose is that the reason for the rot in the first place is water intrusion--in my case from poorly bedded deck hardware. Once the water gets in there, it stays in there. When I removed the top skin on the foredeck what I found was a soupy mess of rotten core mixed with water--lots of it. I can't imagine injecting anything into that mess and having it cure properly. If the rotten area is small, drilling a series of holes and using acetone to flush out the water might work, but for larger areas I don't think there is any way around removing the skin. You are certainly free to do as you wish, but regardless of what you paid for it, I personally think these boats are such a wonderful, timeless design, they deserve to be restored with care.

:: I'm rather sure my deck core is rotten. I know that the
:: best way of fixing this is to cut the deck skin off to
:: remove rotten core, replace the rotten core with fresh
:: wood, then re-attach the deck skin. That sounds like way
:: too much work for a boat that I got off of craigslist
:: for $1200, and honestly, it doesn't sound very
:: necessary.
::
:: I know a lot of people think they can put unthickened
:: epoxy into holes drilled into the deck, but because
:: epoxy runs all over, I've heard this isn't very
:: effective.
::
:: What if I pumped expanding foam from TAP Plastics or the
:: aerosol foam insulation from Home Depot into a grid of
:: holes drilled into the deck skin? Once each hole is
:: filled, I can then fiberglass over the holes. What's
:: wrong with that? If such foam is too weak, what about
:: epoxy thickened with microspheres? Sounds like it makes
:: sense, but evidently nobody on the interwebs has done
:: this and posted about it, so I'm wary of trying to do it
:: myself.