Lor,
I get tired just reading your message!

If it's your only time in Hawaii, why not.
This way if you do go back, you'll know which island where you'd like to spend more time.
Good luck and mucho mahalos!
Kal

I've lived on all 3 islands. The Big Island is named appropriately. It's larger than all the others combined. It takes roughly 2 hours to drive across so if you really wanted to see everything, 2 days is not enough. A few accessable natural attractions on the BI are the Volcano, Hapuna Beach (near Four Seasons), and Waipio Valley. If you go and see the volcano area it will take up almost an entire day. The Volcano Lodge has a great restaraunt and I would definitely recommend dinner there but you would have to reserve an early spot if you plan to drive back to FS that evening.
If you plan on driving through Waimea (which most people do) you'll pass Waipio Valley. Stop at Tex's drive in and get a couple Malasadas (a local pastry) all the local people do. They're delicious with coffee.

Yes, it's silly to do an island for two days, especially the Big Island. I guarantee you'll come away with the same impression we had the first time we went (for three days): "It's all lava flows."

But nothing could be farther from the truth. As we discovered on later trips, there is such a diversity of environments on the Big Island you wouldn't have time to cover them in ten days, let alone two. Yes there are lots of lava flows on the west side, but there are also stunning rain forests on the east and north sides, 13,000' mountains in the middle, rolling green hills in the Waimea area (at 2500') etc etc. I couldn't begin to tell you what to do in two days, personally I'd aim for the stargazing excursion on Mauna Kea (see maunakea.com for more info), a day picnic in Waipio Valley, the Onomea Botanical Gardens near Hilo and maybe a helicopter tour of the island.