As a Nevadan, I should weigh in on this.
Statehood is not something that President Lincoln just dreamed up in the late hours of 10/31/64. It had been in the works for a while; likely since Nevada became a territory after the Comstock strike. Nevada was a true battleground territory just prior to and during the ACW. Unionists and secessionists alike wanted to claim the rich silver and gold deposits of the Comstock and other mine strikes. The contentions got so bad at one point after war had been declared that southern sympathizers were incarcerated at Fort Churchill, Nevada.
The electoral votes were not significant for Lincoln's victory, it turns out, but they could have been. Lincoln's re-election was not assured, and there was concern that he might be a one-term president because of the toll that the war was taking on the nation. So, adding Nevada as a state just days before the election was more of an insurance move than the primary reason why the Silver State came into being. I think it was a reason, but not the reason. Silver and gold were also not the reason, but a reason, too. I'm not sure there ever was "the" reason.
An interesting fact: Nevada's was the first state constitution to be submitted entirely by telegraph for approval by Congress.