I sometimes wonder if some of the people giving answers on here have actually been to places they talk about. First of all, let me correct some incorrect information previously given, Hilo does get a lot of rain, but nowhere near 300" a year...try 70"! As a result, it also is much greener than Kailua-Kona, which is where most of the hotels/resorts are because people come to Hawaii for sunshine, not rain. On the other hand, if you want lush, tropical scenery, you need rain!
The other benefit you get when you have rain is that you get waterfalls. There are two in particular that are easily accessible near Hilo, Rainbow Falls and Akaka Falls. On the west side of the island, not only are there no waterfalls, there are no permanent streams or rivers...just those that occur when they do happen to get a heavy rain.
If you are interested in visiting the Hawaii Volcanoes National Park, you would do best to base your stay on the Hilo side of the island. That could be in Hilo, Mountain View, Keeau, Kurtistown, and Volcano Village.
And, while it is possible to drive around the island in a day, it is not advisable unless you just want a windshield tour of the island. You can easily spend a full day or days exploring the Volcanoes National Park and its uniqueness makes it well worth the effort. In this one location, you can see endangered native species of birds and fauna, an excellent field of Hawaiian petroglyphs, and, if you're lucky, an active volcano. (I say lucky because while the eruption has been continuous for quite some time, it is not always in an area that is accessible for viewing.)
If you take a drive to the eastern end of the island, pass Pahoa, you will find a few nice black sand beaches, although, they are frequented mostly by locals. I would recommend going Mon-Thur and leaving it to the locals on the wknds to minimize the chances of running across some of the less-than-friendly types. (Always go with your gut, if you're not comfortable with those around...leave!)
Or, you could drive about 30 miles beyond the HVNP entrance towards Kona and stop at Punaluu State Park, a black sand beach just a mile off the main highway. No food facilities, but restrooms and a covered pavillion is there, if not already in use. The Hawaiian Green Sea Turtles love to frequent this bay and beach for both food and resting.
I invite you to go to my blog, www.myhawaiifoodfun.com, and view the posts on A Drive Around The Big Island (Parts 1-3) for more information, as well as my website, www.myhawaiionline.com/islands.html and click on the Big Island for more information that you might find helpful.