Spark Plug Replacement Time Interval

[lamesacarrera]

I'm wondering if I should replace my original spark plugs. Car has 20K and it's just over 4 years old. The manual states plugs should be changed at 4 years or 60K miles.

It is a 2002 C2, 3.6L.

Also, I've had some recent trouble with huge smoke clouds out the rear of my car during spirited club drives. It's happened twice. No redlining but I was running it at 4-5,500 rpm more often than usual in the twisties in the San Diego County mountains. The first time this happened was 1200 miles ago, I was able to drive it home ok and the next day the dealer replaced the oil separator valve under warranty. Then it happened again a week or so ago, bigger smoke cloud than previously (roughly 40x20 ft). Whitish blue smoke, definitely oil, not coolant. I was able to drive it home without any trouble. I did have smoke upon startup the following morning on my way to the dealer. This visit resulted in them telling me they couldn't duplicate the problem, oil separator looked fine and couldn't find any problem. They test drove it several times, ran it up to 5000 a few times and kept it overnight to get a cold start observation. It hasn't occured since in the past week since I got it back from the dealer. I doubt this could relate to spark plugs but I'm a layman trying to think of everything. This is unsettling because the car is now out of warranty as of a month ago.

Thanks for any insight!