A little pricey for some maybe. May have done better with regular plugs and wires, don't know. I had the cash so why not. No real dyno number's so I can't say for sure what the difference is. Every so often I drive up to Auburn on 80 or up to Placerville on 50, both freeways have several hills and valleys to climb. Before the upgrade, truck would shift in and out of overdrive to get over the hills, now I am able to maintain a steady 2000 to 2500 rpms without having to give it more gas. Passing ferds and chebbys up the hill I roll down my window and yell 'GET A DODGE' lol.
As your regular tune-up parts age (plugs, wires, filters, etc.) your performance slowly decreases. So by performing your basic scheduled tune-up with regular stock products, you should notice an increase in performance (not greater than original, but better than before you did the tune-up when everything was old). There are plugs and wires and filters, etc. that are made to increase performance and extend the time between tune-ups. For example, k&n's drop-in filters aren't made out of paper like the ones you pick up at your local auto parts store, they will never have to be replaced, just cleaned every so often ~ I found a slight increase in gas mileage, nothing drastic, but in the end i'll save money on filters because I don't have to buy a new one every few months (i live in a dusty area so I would be going through filters like water).
Standard copper spark plugs should be changed every 30k miles. Platinum plugs have a longer life of 50-60k and perform better than copper. Iridium plugs rave a life of 90-100k (manufacturers say change at 60k, but you can pull them out and take a look and you should be able to go a lot longer) and perform better than platinum. I have a V6 with zero hand room and manifolds that have to be removed in order to get to the plug cylinders, so for me, changing my plugs is an 8 hour job and it is totally worth it for me to pay the extra money just to be able to change them as rarely as possible. I did also notice a slight increase in gas mileage, but others dont notice a difference. But if I had a 16 cylinder Hemi, I might change my tune.
So I guess you have to decide what is best for you ~ some enjoy changing their plugs and its a quick and easy job, so they like to stick with copper or platinum. Others feel its worth the extra money to not have to change plugs that often, or that the cost of paying for iridium plugs is a lot less than paying a mechanic 3x as often to change the plugs. Just have to judge for yourself.