Woops - forgot to update this thread!
Better late than never, eh? Basically, it was a non-issue... extensive dragstrip testing has proven that the car is running normally for a 500E, at my elevation (2700'). At a sea level dragstrip, it was faster (as expected), and I also had traction problems when launching... indicating improved low-end power at lower elevation.
However, the temperature-related power drop remains... when the engine is cold to cool (say, 50-70°C on the dash gauge) the car will spin the tires much more easily. At 90°C and up, it will only spin the tires if ambient temps are fairly low (say, under 60°F). When I originally started this thread it was in the middle of summer heat (July) and the car pretty much refuses to spin the tires in summer, unless engine temp is ~60°C. I wish there was a way to produce that "extra" power at normal operating temps (80-100°C) but I doubt that will happen as long as the LH engine management system is in control. I believe this is "normal" and there's probably nothing wrong with my car. (If yours will fry the tires on a hot summer day with no problems... then maybe I
do still have something wrong!
)
Hope that helps - let me know if you have any more questions. I'm still planning on a dyno run.