Well, done with the install. At last.

I couldnt stress how much better the system sounds over stock... Still, Ill keep upgrading over the next few months. Next up is an amp/sub. Im in absolutely no hurry to do this, and Ill likely have someone build a nice box so I can mount a 10 inch sub in the rear spare area... Ill likely go the 3 channel route with the amp (so as to also power the polks in the front, likely with ~60 or 75W RMS)... Im not planning on anything overly expensive. Any recommendations on amps that will fit while well hidden?

running new wire from where? All the way to the HU? Man that seems like a LOT of work.

When I would change speakers back in the day, Id just pull the old one out and wire the new one in using the existing wire. This is frowned upon now?

Keep in mind, Ive not installed a system in 15 years.

I have a Pioneer 4200NEX and have the itch for some better sound. No subs, just nicer speakers to attach to the HU. I wont be amping. Im not crazy into this...just want some richer sounding music

My comment was for rear speakers. Sense the base model doesn't have rear speakers there is no pre ran wire back there. You have too run new wire from the head unit to your rears. As for old school yes back in the day it was easier. But today there are many differences such as separate tweeters and woofers (front speakers) that make it hard to use the new crossover included with the new component (again front) speakers. If you have a bose system that has it's own set of issues such as speaker wire isn't running to the radio, its being ran to the trunk to an amp.