Spark Plugs... And other issues?

So I recently had my car in the shop due to an issue with bucking/hesitation under anything but light driving at boost levels of about 5psi or higher.

 

 

 

Shop wanted to do a compression test and ended up find my plug(s) pretty yucky, new plugs fixed the issue.

 

 

One plug looked pretty bad, with the center electrode being pretty corroded. Is there anything telling from these crappy pictures the shop took?

 

 

The compression test results were as follows:

 

 

Cyl 1 - 140 psi

 

Cyl 2 - 135 psi

 

Cyl 3 - 135 psi

 

Cyl 4 - 120 psi

 

 

Which is amazing since the previous compression test/leakdown results 3 years ago were..

 

 

Cyl 1 - 127psi / 0% leakdown

 

Cyl 2 - 130psi / 0% leakdown

 

Cyl 3 - 127psi / 0% leakdown

 

Cyl 4 - 129psi / 0% leakdown

Suppose this is a good place to pose my Question. My Legacy 2.5i is 8 years old (2010 Legacy), Im a little over 198,000 miles on it currently and I believe the spark plugs have never been changed. I have no issues with the vehicle running, no power lag, no misfires, etc. What is the average life span of spark plugs? What brand is recommended to replace with?

60,000 miles is the recommended mileage to replace the plugs. I have gone 80,000 miles before I had a misfire.

 

I only put NGK's in my cars.

Does 60,000 miles apply to NA 2.5i engines too? I just noticed mine is not idling as smoothly as per normal.

Just re-read above, thanks.