I can see the argument for dealer stamps if you're going to sell within a few years, but for a car which you want to keep and be sure everything's been done properly then you need to either do it yourself or take it to an independent who you trust.
We bought our Defender in 2002, paid around £14.5k for it IIRC. It's never been near a LR main dealer, has no stamps at all in the service book, and we've been offered £18k for it. We chopped our Fiat 500 in against the Mini, they dropped £500 off the value as it had no main dealer stamps. It was a 7 year old car, and the main dealer service costs would have been far more than £500 over that time.
My Morgan must be practically worthless on paper as it's been so extensively modified from original, but to an enthusiast who knew what they wanted and understood what they were buying, it would be a good bet. No amount of service stamps would make any difference at all.
