The attacker, 22, scored twice in the first half as the Partenopei defeated Fiorentina 3-1 at the Stadio Olimpico on Saturday to claim the domestic trophy.
Insigne has been mentioned as a potential pick in Cesare Prandelli's 23-man Italy squad this summer after an impressive season at the Stadio San Paolo and Benitez believes it would be foolish not to take him, as well as stressing how well Napoli played in the cup final.
"There is talk of him going to the World Cup and I say without doubt he should go, as he can make the difference in any game," he told Rai Sport.
"We knew that we’d all win together or lose together. I am very satisfied with the performance. Fiorentina are a strong side and we worked hard to beat them.
"I think it was a beautiful game. We were in control at the start with 2-0 and it seemed simple, but then Fiorentina got back into it. We could’ve got a third goal earlier, but we also worked well in defence and with 10 men did well as a team with real character.
"I have always said losing wouldn’t change anything, a win would be more positive. The fans saw that the team played 100 per cent and that’s the important thing."