Think with the older coupes I'd go indie every time, they work on them day in day out and therefore know them inside out, whereas the MD mechanics do not. Would think it is a different story with GTs though so get some prices and see who is willing to match or beat the best price. Agree re the stamp, don't think an indie stamp would put people off buying.
My view is that you need to take a car to somewhere that regularly works on that model hence why 3200 and main dealer don't go well together. The good thing about long Maserati life cycles is that plenty of specialists have lots of experience of working on the same/similar cars. After all the QPV and GT/GC are all very similar.
I do think places like Emblem, Shiltech and Migilore are excellent indies. I am sure there are others as well. I have happily used both indies and main dealers.
But I don't really agree with the arguments that Main Dealerships need to see a car week in week out to be able to provide an excellent service. If you've ever walked round some of the well known Main Dealerships, you wll know what am talking about.
The last time I did I saw an F40, F50, a Dino, a 275, a 458, a California T, a Testarossa, a F355 a few F360s, a number of QPs, a few GTs and my 4200. Quite the spread! They knew the foibles of my car and I am sure the others as well. I doubt they see an F50 every week, every month or even every 6 months given there were only 350 made.
Don't forget the level of experience, training and equipment the more senior mechanics at these places have seen.
I am sure a F40 owner could afford a few more of the nice-to-do items rather than the must-haves. But few people get rich by being a fool and letting someone overcharge and pull the wool over their eyes. I also would imagine they demand a high level of service.