How important is...

Resolution.

Really, how important is it to have a 1280x720 over 800x480, or is the pixel density more important?

I'm in debate over what phone to get out of the new crop of devices, and I'm even considering a lower end device depending on how much the high end devices are going to cost me, unlocked.

So how big of a difference, in all reality, is the impact of screen resolution in relation to the Nokia 920 and 820 or the HTC 8x and 8s?

To be honest, after qHD everything looks the same to me.

Just bear in mind that, Windows Phone 8 apps will probably be made in 1280X720. 800X480 will look exactly like your current Windows Phone or Galaxy 2, it looks good.