[240 2NR]

Well if there is no evidence of them ever being replaced, you may be in luck actually.  You may feel the difference in performance and be one of the statistics where new wires really do make 10hp.  Maybe not, but you're still WAY overdue for the change.

As said above, it's fairly cheap and very easy.  A wire, cap and rotor swap will take 30 minutes, but don't rush it.  
New wires are the most expensive at $50, the cap and rotor are like $7 each at courtesy nissan.

Two things to watch out for are that the rotor goes on two ways, the right way and the wrong way, so just watch and make sure you put it back on facing the same direction it came off and you'll be fine (it would actually be pretty hard to screw up, unless you didn't even look at the direction it was before you took it off).

The other thing to note is that the cap is not in order.  As you go around the order is 1,2,4,3.  Just make sure you don't assume it to be 1,2,3,4 and wire them all in sequence (it's all marked on the cap as well).