A 7 day Japan Rail Pass would certainly be worthwhile in this situation. As the price would be cheaper than purchasing two single fare tickets between Tokyo-Kyoto. As long as you make the return trip within 7 days.

Restrictions with the JR Pass:
You have to purchase it outside of Japan (travel agencies etc sell them), they give you a voucher for the pass, when you get to Japan you can exchange the voucher for the actual pass.
You cannot use the pass inside Kyoto itself on the municpal subway or buses.
You cannot take the Nozomi Shinkansen, but you are free to take Hikari Shinkansens between Tokyo-Kyoto.

But it is still worth it if you want to save a little.