Nice write-up. I have a couple of things that I would like to address, coming from my own 8500 miles worth of experience on my '09 (I came from an '05 Saabaru Stage 1):
The suspension felt squirrely to me especially while rounding corners on severely rough surfaces for the first couple of thousand miles, but to me that seemed to soften up later and I don't consider it to be a problem now. I'm not sure if it was the suspension settling or if I just modified my driving style. Havv you have noticed any changes in the way the car handles after putting a few more miles on it?
I have also experienced the same sustained revs after letting off of the gas and pressing the clutch quickly in stop-and-go traffic, but I didn't assume it was a bug. On the contrary, I assumed it was a 'feature' that the car company 'included at no extra charge' similarly to the way we have the hill start assist. My dad's Toyota truck does a similar thing, and I think my grandma's Saab 9-5 does it, too. It used to annoy me, but I changed my driving style some and now it happens less frequently. I don't have a large commute through a lot of stop-and-go, though.
I have the same gripes with the seats. I would have liked leather and some more bolstering, since I'm not your average McD's booth-filling American, but I'm not apt to complain too much. Had I bought an STI and then needed to get sportier seats, we might be having a different discussion...
There is one thing I will outright and completely disagree with you about, though, and it is the visibility out the rear of the car. In my opinion, the 5-door has better rearward visibility than the 4-door. And, I had a rental Ford Fusion for a few days before I got the '09 WRX, and that was just abysmal. The rear view was one of the selling points of the hatchback to me. But, this is my opinion, and my '05 was a wagon, so I don't have the sedan experience that you do.
I felt the same way about the sound quality in the car for the first week that I drove it, but then after much mucking around with the radio I finally turned off SRS and BAM! it was only half as crappy as it was before. It's still crappy, but it's tolerable, especially since I listen to talk radio and talk podcasts in the car, and save my music listening for the jambox at home.
My big question: you made reference to a 'black box' for interfacing your steering wheel controls with your Pioneer deck. I have been considering making the move to something like a Pioneer AVH-P4100, and I have seen people talking about using a PAC SWI-PS for interfacing their steering wheel controls with their Pioneers. Is this what you're using, or do you have a different solution. I was reading people complaining about the delay between the time you press the button on the wheel and the time that the HU registers the command. Do you notice this with whatever solution you are using?