Will changing spark plugs really get me some better gas milage?

depends on the plugs, the best plugs i have seen for better gas mileage are the E3 plugs. they are about $6 each. Platinum plugs have a small increase, usually not noticeable, same with double platinum plugs. Iridium plugs also work well, but nothing seems to compare to the E3 plugs. I have seen a 4 mpg increase in for rangers with a 2.3 and a 2 mpg increase in the H2.

I disagree with the above poster. The plug has very little to do with the efficiency of the combustion cycle. Unless it has abnormally high resistance or is gapped incorrectly it'll perform nearly identically. Most the time anyone 'sees' an improvement they are replacing old with new and the gains are due to having a plug with no fouling. Lower resistance plug can make negligible gains but are usually copper cores which don't self clean, which is why you tend to only sees these on track cars anymore. Iridium is in between platinum and copper and self clean but are too expensive to justify their cost for negligible gains. Any decent platinum plug will work and should be self cleaning. IME and IMO there is nothing worth noting between brands and you should just get whats readily available. I generally use Bosch simply because they are cheap, readily available around here, and get the job done.