The best way is to calculate the trips in between and see if it makes up to the cost
but according to what you said it's not worth it to get the JR pass.you can use http://www.hyperdia.com to calculate your JR train rides and see if it's worth it.
The rule of thumb generally is at least 2 shinkansen rides for the 7day pass, but if you are taking loads of ltd express trains in between you may be able to make up to the amount.