First of all, don't count on seeing any lava from the ship. The Infinity went around the north end of the island, you would have to go around the south end to see the lava. Also, not much of a lava flow when we were there.
Having said all of this, I would very much encourage a helicopter tour. We took Blue Hawaiian helicopters from Hilo airport, about a 50-minute flight which will cost about $140 each if you book over the internet, and you are not over 250 lbs (they check). It was a great experience. Our ship left Hilo at 3pm, so not time to do much else.
We also took a helicopter tour on Kauai with Island helicopters. Must more impressive and senic than the Hilo tour. If you can offord it, do them both