LN's video with Tony Callas talking about fuel trims was very helpful:
https://www.youtube.com/watch?v=HW7BmBIJDXs
He's pretty clear that fuel trims at idle (RKAT) are typically vacuum leaks, and trims off at cruise (FRA) are usually fuel delivery issues.
This thread by Ike84 also helped a ton, and I'm usually better with long forum posts than I am with youtube vids:
https://986forum.com/forums/boxster-general-discussions/81522-causes-lean-conditions.html#post640946
I definitely fell victim to thinking that the car was rich. Lots of things cause lean with these cars, which makes the DME go rich trying to compensate.
My car also had intake backfires, gassy rich smelling exhaust, and high fuel consumption, and in the VW days I'd look at that and say it was rich. Well, the DME knows the data, and when you make it spill the beans the truth becomes clear.
I put some more miles on the car this morning. The trims still look pretty good!