Hey, thanks all for the replies.
First, dieseldiehard, this degradation has been increasing over 4 years or more. I have complained (search for my id) about severe performace problems off the line at high altitude (Denver) since I owned this car. It would seem to make sense that if the ALDA is providing fuel a bit light at sea level it would be exagerated at altitude. It just keeps getting worse.
Nevertheless, I want to investigate the wastegate issue that you have identified. Can someone point me to a picture of what I should look for? I know that when I changed the head the soot buildup inside was shocking. It's perfectly reasonable that I have something cracked open that's robbing boost preasure. I'd love to find it and spend some time cleaning it out, but it's not clear to me where to find this problem.
As Lukejt and Brandon suggest going from a lean ALDA to a properly adjusted one should have no impact on fuel economy. How fast and far you go takes the same amount of energy no matter where your ALDA is set. The difference is how far you have to hold the throtle down to get enough fuel to the engine. Of course, sending unburned fuel through the engine is the same as a leak. Economy will suffer.
And finally, Busybenz, I live in an urban area, and find that 0-50 accelerations attract a little less attention and I can squeeze them in between lights on the west side highway of Manhattan.
Thanks,