You may like the independent idea, but you have to place yourself in the shoes of a potential buyer. Like it or not, most people will prefer a dealer serviced car as that defines a standard level of service. Independent service levels can not be verified by buyers as they have no idea that the bloke under the arches is any good or not, so they will assume it will have be done as it is cheap.
Unfortunately, my experience (from others) with independents is that all I see, is the cars going backwards and forwards to fix the same issue over and over again costing in the end more than what a dealer would have cost.