I have about $500 less than that invested with SUPERB clarity and overall sound with no audible distortion regardless of volume level. I did it over time, as budget allowed, not in one chunk. Those improvements include Polk speakers, JL Audio Clean Sweep, 12 gauge wiring, JL Audio Amp, sound absorbing mat (can't remember the name) in front doors and rear shelf, 200W 10" Bazooka Sub, and ALL professional installation. My point being that you might want to shop around a bit.
Many have been well pleased with the addition of a self powered sub to a completely stock system at a cost of $300-350.
You've got to make a decision regarding budget and how important your tunes are to you.
