I will agree that there are a great deal of incredibly lazy shops out there, and in my experience, dealerships are absolutely some of the worst.
Which car were you told they had to mess with the suspension to remove the gas tank? There is no W-body where touching the rear suspension is required for tank removal. As for your Achieva, I can't speak for NH's smog laws, but there is nothing complex or unusual about the exhaust on a N-body, Quad 4 or not.
My point was really that you can't get any more dead-nuts simple than a 2.8/3.1 1G W Car, and I would take a shop telling me "yeah, it's too old and we're too inept to open up AllData, so we're just going to tell you to get lost" as a dodging a bullet. I'm sure those same shops would be more than willing to diagnose issues on a 2003 Grand Prix SE, which is virtually the same car with nearly the same powertrain.
If a shop can't properly work on a pushrod 1G W car, they shouldn't be working on anything.