I've not quite hit 50K on EITHER my wife's 04 325Ci or my 06 3.0 X5..

I wasn't planning on EVER replacing the plugs since at the rate we're going it'll be another 5-6 years before we are even close to 100K (the recommended change point).

Is there any value in changing them early ? mileage, power, etc or is it only noticeable on the 4.0+ engines..?

ed