When to replace those plugs?

This question is about spark plugs and preventative maintenance.
My old man told me that in general, you should always replace your plugs and wires every 75,000 miles to maintain the best gas mileage and performance. My mechanic told me that you should only replace your spark plugs when they need replacing. (Do you wait until your car runs like crap?)

Personally, I like being proactive with my vehicle maintenance. Does anyone know any pros & cons to my old man's point of view and my mechanics? What do you do?

And if you want to know, I drive a 2000 Pontiac Grand Prix GTP.

Twenty years ago I used to change my plugs every couple of years, now with the better technology and different types of long lasting plugs available I usually change them before the time they are "supposed " to last. I don't let the plugs stay in my engine for 100,000 miles, rather I change them out well before that. The longer you wait to remove them some issues could develop such as a harder time removing them. Granted on many vehicles today it is a lot harder to access the plugs, especially the rear ones, but nevertheless, they should still be changed on a fairly regular basis before any issues crop up. I also use anit-seize compound on the spark plug threads and dielectric grease on the inside of the spark plug boots to make it easier to remove the spark plug wires from the plugs the next time you need to do the job. I've seen spark plug wire boots literally "weld" themselves to the plug and many times the wire was damaged in the removal attempt.
The way I see it, plugs don't really cost a lot of money in most cases. and replacing them with a new set on a regular basis is a good practice to keep your emgine running good and to obtain good fuel economy.

This question is about spark plugs and preventative maintenance.
My old man told me that in general, you should always replace your plugs and wires every 75,000 miles to maintain the best gas mileage and performance. My mechanic told me that you should only replace your spark plugs when they need replacing. (Do you wait until your car runs like crap?)

Personally, I like being proactive with my vehicle maintenance. Does anyone know any pros & cons to my old man's point of view and my mechanics? What do you do?

And if you want to know, I drive a 2000 Pontiac Grand Prix GTP.
I'm with you...I like to replace plugs BEFORE they're bad. With standard plugs, I would replace them every 30,000 miles (wires every other time). With platinum plugs, they'll last longer so 60,000-100,000 is possible. Today's transverse V6 cars (yours and mine), pushing the change interval back will delay the stress on you...so put in good plugs and change them as frequently as you can handle (60,000-75,000 sounds like a perfectly fine range).