IMO, to way to go is to self service. The reduced cost is considerable. You can write down everything that is done. In 17 years of car ownership I have never paid for a service, ever.
The only things to be changed is oil and filter, the rest is 'checked' - a monkey can do that - if it actually gets done.
So if you service the car and save per service. So, after a few years and services, is the increased value of having a dealer stamp going to match that absolute saving?? Probably not. To be perfectly honest, the dealer stamp means nothing to me. Based on my experiences of Fiat dealers, the stamp would be detrimental, I'd prefer to see an independant stamp there.
At the end of the day, does to cost justify itself and I don't think it does. my car has the service due indicator on, has done all the time I've had it. Bothered? No. Warranty is so poor anyway, it sometimes seems to be a pointless piece of paper.
And I am not overly negative about dealers - just realistic based on my experiences for the last 17 years.
Bottom line - dealer service is overpriced . . . . . fact