Do we need travel insurance?

As you know, the four of us will be going for our annual vacation in December. I was wondering if we need to get travel insurance. In addition to possible flight delays, cancellations, lost baggage etc... I am more concerned with the medical aspects of things. Will we be able to get the necessary medical assistance in the event of a travel emergency? I mean we will be driving 4 1/2 hours from Los Angeles to Las Vegas after all.......