I think Nixon shouldn't have made his pledge to campaign in fifty states, since that led to him having to campaign in states he had no chance of winning or states that wouldn't matter.
Yes, you are absolutely correct.
This is another very serious error in the 1960 Nixon campaign.
Because of this pledge, Nixon was campaigning in the latter stages of the campaign in such states as Alaska, already safe for him, while Kennedy was campaigning in places like New York and Pennsylvania.
In the final analysis, however, don't forget Kennedy got 303 EV to 219 for Nixon. It would have been extremely difficult, if not impossible, for Nixon to have made up an additional 50 EV in order to win the election.
Rockefeller could have helped.
Advanced civil rights plank could have helped.
Not campaigning in all 50 states could have helped.
But 50 EV is a lot to make up.