So did the VW repair shop say that this was abnormal? B/c every car does this when started cold. They basically have an electronic-type of choke where there is a rich fuel mixture to get the car going. Then the idle slowly falls - as you say - over 1/2 to 1 minute or so and approaches its normal warm idle speed.
What you want to do is find out where the car should be idling when it is completely warmed up. These days the normal range tends to be anywhere between about 650-900 rpm. 1000 is on the high side, and 1700 is certainly on the high side for cold start up.
So if there is a problem it isn't that car idles higher at start up - its supposed to. Its that it is idling a little high to begin with, both at start up and after warming up. A small vacuum leak can cause that as can a sticking or malfunctioning idle air control valve. Your throttle body and throttle plate are also worth a look.
The secondary air hose that they referred to is likely a factor mostly when the car is cold so I wouldn't necessarily look there. (And I'm not surprised that it made no difference). Look for an idle issue, not a cold idle issue.