Spark Plugs

I have a 2000 Subaru Outback with 114343 thous and a 2.5 liter. My problem is two fold. My car lags sometimes when I accelerate almost as though I were about to flood it. I thought about changing the spark plugs and was disappointed to read in the manual that basically "it might be too hard for you so just go to the dealer". It was if they knew me. After I finally actualy found one of the spark plug caps and drew it out there was a good amount of oil in there. I replaced the cap and the car started and is running as before, but was that normal for all that oil to be in there? And what can I do to help with the lagging as I drive?