I have lived on the Big Island for 24 years and the only real climbing on this island would be down at south point, as people have mentioned before.
I did do some bouldering above water,, low water soloing, at the ponds above rainbow falls. Only safe at low water.
Most any thing that is solid enough to climb looks like you could slice off your fingers on the holds. Most of the rest is old rubble.
There might be some stuff if you spent a lot of time exploring the gullies along the Hamakua coast. Just be sure to bring tons of mosquito reppelent. There are gullies on the dry side too. Along the highway between Kawaihae and Hawi. Just be careful of the thorns on the keawe trees. No walk in the rubber slippahs... you get one puka in da foot.
For Kauai I would second going up to Kokee and hike to the Ko'o'lau look out.
Edit , yo, Joey how's things in the nuke free zone :)
If you ever make it to the big island I will buy you a beer.
Not me of course, the road crew. Kind of an epic project on the 2 lane highway full of tourists and p.o'd locals...
Thanks for the offer...all's well in west county...Huge casino being built in Rohnert Park(ugh). SMART rail progressing...