Gerrycan

I tend to agree with the sensor issue theory although I remember carbon build up could cause some pinking in old cars.

Did not change them myself, I just had them changed at the major service for my 1.4tis at about 50k km and 5 years. I did ask for the old spark plugs to be kept so I could examine wear and they did. Quite honestly the plugs were showing hardly any wear, I think they could have done another 20k+ km with no problem at all, but it was a relatively minor cost although I did not notice any difference in performance. This is not a high performance engine so any genuine spark plug you mentioned will do. As an aside, a few years ago I retrieved an old Toyota Echo from from my daughter who was issued a company car (Golf GTi) and the echo had missed a 'few' services so I undertook a major service myself. The standard spark plugs were incredibly worn and about 3x the recommended space. I was somewhat disappointed there was no subsequent noticeable change in performance or economy. In short if your car is going ok at the moment then do not expect too much when you change the plugs.