The huge discrepancy between dealer service neve ceases to amaze me. I think your story is all too familiar, but we all also have stories of superior service at other locations.
1.) When I had my Nissan GT-R, they would drop everything and get you in and out, as long as you had an appointment and the GT-R tech (usually one per dealer) was working.
2.) We have two local Mercedes Benz dealers, one about 15 mins farther than the other. I always went to the farther out guy out of habit. They were great. Always had a new MB loaner for as long as you needed/wanted it. No hassle, no paper-work. I thought I would try the other dealer. I let them know I needed a loaner when I made the appointment. I show up at the appointment and they look at me all crazy when I ask for the loaner...they say that I can rent one from there "rental" desk which is a card table with a 18 year-old-girl sitting at it....I finally got the car (for free), a 4 year-old stripped IMPALA which was filthy!

What really amazes me is that the dealers don't take this opportunity for free advirtizing. You have a CURRENT BMW OWNER's full attention. Give them a great new BMW to "test-drive" for the day. Ask them what they would like to drive..."Oh, I see you brought in your 3-series wagon today, maybe you'd like to drive the new X-3 for a few hours, I'm sure you'll really enjoy it!" The customer comes back to their 5 year-old 3 wagon after speding the last 5 hours in a brand-new X3 and you just might have a new car customer! Seems simple....

Obviously this is a passionate topic for me.