Hi there,
The general rule of thumb for buying a 7 day JR Pass is that it is worth buying if you do 1 return trip from Tokyo to Kyoto (¥26,840 return).
You can use the JR Pass to travel to Nara, Kobe and Kansai International Airport, so it's possible that a 14 day rail pass will be worth it for you. To decide if it is worth it, you need to make sure that the ticket costs exceed the ¥45,100 cost of a 14 day japan rail pass. You can check on individual ticket prices at the travel planning website hyperdia.
I'm not sure from your question how many trips you intend to take (for example, I'm not sure if you are doing more than 1 tokyo-kyoto trip), but for your reference, here are the costs of the legs you mention:
- Kansai airport > Kyoto: ¥3690, (75mins, 99km)
- Kyoto > Nara: ¥690, (49mins, 41km)
- Nara > Kyoto: ¥690, (46mins, 41km)
- Kyoto > Kobe(hyogo): ¥1050, (56mins, 75km)
- Kobe(hyogo) > Kyoto: ¥1050, (55mins, 75km)
- Kyoto > Tokyo: ¥13420, (161mins, 513km)
- Tokyo > Kyoto: ¥13420, (165mins, 513km)
- Kyoto > Kansai airport: ¥3690, (79mins, 99km)
TOTAL: ¥37700 for 8 legs
Based on these legs, a 7 day rail pass is certainly worth it, but you will need to ensure you do some more travelling to make a 14 day rail pass cost effective.
Hope this helps!