I've been told I have the wrong plugs in my car. The mechanic said the plugs should be some 100,000 mile plug that's rather expensive. Is this the same plug as the oem NGK Platinym plug?

yup yup
 

NGK Platnum is the only way to fly.

Other plugs will probably work okay but
 

you not get the 60,000 mile change intervals out of them. since they are kind of a pain to get at, I suggest the Nissan NGK plats. Courtesy Nissan is a good source for discount prices.