Aside from a feature list that might be attractive to some it seems that video performance technologies involved are pretty much the same, any audio performance changes would only be due to wattage increases, and build quality would be same throughout...(correct me if wrong)
you are correct that audio quality / build quality is the same from the 59x/16xx up to to the 89x/23xx level.
you are incorrect that video performance is the same; in fact that is one of the major differentiations between the different levels. I explain the differences more specifically in the FAQ in post #4 of this thread.
I don't have personal experience with Pioneer but if you do some searches you will find many comparisons. Audio/build quality should be pretty similar, a lot depends on whether you prefer the Audyssey setup or Pio's MCACC; the Elite Pio's will probably have better build quality though. The 1020 will not -- you can walk into Best Buy and see for yourself if you want to feel how hefty they are (the Pio 1020 on down isn't).
The Denons from 79x/19xx on up will have slightly better video performance; you can read CNet's reviews for a comparo of the 1910 vs Pio 1019 in terms of video.
AVR will be running Polk Monitor 70's/CS20 which I understand likes to come alive when fed clean power...Is there something else I should consider?
yes, you should consider better speakers, since audio performance is your stated first priority. Those are essentially entry-level Polks; if your primary goal is improved audio performance you would be better off buying the cheaper AVR and instead sinking that money into a really nice subwoofer or upgraded speakers.
Stepping up from, say, the $349 AVR 591 to the $849 AVR 2310CI will gain you almost nothing in terms of audio quality, it will all be about additional features. But take that $500 and put it into your subwoofer budget..... now we are talking!