I would agree with two exceptions:
1: If the car is in need of a diagnostic and you can't figure out what sensor or module is wrong. $70 at the dealer who has an interest in getting the car out ASAP and has all the equipment to test every module and sensor on the car is a cheap price.In my case, I recently had a car in a shop for two weeks and he couldn't figure it out. Then I took it to another for a week - and same deal. Took it to the dealer - 3 hours later(charged for 1.5 hours) they told me what two things were wrong and also changed two things the second mechanic altered to get it to run back to where they were supposed to be. Wouldn't run anymore after that, but with the two *proper* parts installed - presto!
Small shops arent set up to track down electrical system gremlins as quickly and efficiently. Of course, all dealers aren't the same, so YMMV.
2:One area that I found to be worth going to the dealer for was replacing the door seals. Why? Because half of the time it still doesn't seal correctly and has to be replaced again or altered. The dealer will eat the inevetable couple of improperly installed attempts/pieces to do the job right(especially true if you have the older foam type). Definately not a DIY job. You only pay for the one correctly installed set, no matter how many pieces it takes.This also holds true for parts that tend to destroy themselves when you are trying to install them(sunroofs come to mind - a PITA to fix).