Should I get the 21 JR pass?

Hi,
I'm planning on a 3 weeks trip to Tokyo, Nagoya, Kyoto and not sure whether or not I should get the 21 days JR pass. Here's my itinerary:

I will be coming in from Narita Airport to Minato
7 days in Tokyo visiting: Harajuku, Yoyogi Park, Ameyoko, Akihabara, Meiji Shrine, Tsukji, Ginza, Shibuya, Shinjuku

14 days in Nagoya/Kyoto: Gion, Nishiki, Chion-in temple, Sanjusangen-do Hall, Kinkakuji, Ryooan-ji

your insights would be much appreciated!

Thank you,
Wendy