it's not a matter of plugs being good or bad, it's a matter of them being a wear item. THink of how many little sparks dance across those electrodes over the course of "only" 37000 miles. YES they make plugs with 100K claims and there's no reason they won't work thatlong, BUT>>> will they be in optimal shape? think about it, nomatter what kinda iridium, or platinum or whaever they coat the thigns with. sparks arcing across metal is how you weld things, and also a very effective way of cutting metal. And that isn't even getting into the heat stresses the things are put under...
Basically, in The end, a set of spark plugs is CHEAP!!! gonna cost you MAYBE $20-30. and chances are you can get the parts store to gap them for you... I PROMISE you it's not much of a hassle to change plugs.
However when you get them, don't get lured into the performance plug game. factory NGK's are where it's at. no sense wasting extra money on marketing gimmicks.
I'm not saying it's going to without a doubt give you 5mpg. but It cannot possibly hurt, it can only help. You'll look at the old ones and be relieved you replaced them.
IF you're looking at eliminating possible economy-robbers, this is towards the top of the list.