My 2003 2.6 manual has steadily had all the usual things done to it to get it up to a decent standard.
Today I changed the spark plugs, but have previously done all the filters. Daz dropped the sump and gave it a clean out, then new oil and filter.
When looking at the plugs today bank 1-3-5 all had NGK plugs in, all rather black and tired looking. Bank 2-4-6 had NGK in 2 and 4 and GM in 6. In the service history there is a bill for a full service from VX including the change of all 6 plugs about 18 months ago. I was suprised to see NGK in there, and plug 6 being GM. So I suspect VX didn't change them and just charged for it, and whoever put the NGK in, couldn't be bothered to do plug 6

Pretty poor I think, but after 6 new plugs fitted, I have noticed quite a difference, much better when starting and generally seems more responsive, albeit only very slightly.
I went through the history the other day and saw when the car had done 41k miles a replacement cambelt tensioner was fitted, but no mention of any other cambelt item at the same VX dealership.
When Daz did the cambelt the other day, both banks were 1/2 a tooth out and there appeared to be plenty of slack on the belt, so another thing that hadn't been done properly.
But after all of this MPG has increased from an average of 26.3 to 34.7, much smoother idle and just much better to drive. I know we all know the importance of keeping our vehicles serviced, but it really does make a difference.