I think the advantage of going to a main dealer in my eyes is purely down to the fact that if they properly shag your engine or cock up your timing you can get it fixed entirely at their costs. God knows I don't trust their technical knowledge.
Going to an independent is a bit of an unknown entity and if they balls it up and refuse to pay you've got a fight on your hands.
I would say the complete opposite. Everyone has seen the lengths that dealers will go to to get out of repairing things, changing things or doing anything else that ultimately ends up costing them money.
If they screwed something up, I would say they're far less likely to just own up and fix it.
An independent / specialist is someone who is likely to be in business not because people feel they have to go to them (as they do with a dealer), but because people choose to go to them, most likely because of their reputation / word of mouth. If they screw something up, they'll more likely be willing to fix it because they know bad worth of mouth is more likely to affect their business.
Just my 2p.
Either way, there's no way I'd go to a dealer for this work.