I have a new 2010 WRX. My 2 previous behicles had premium Bose systems, so the WRX audio was a huge disappointment.
After reading this forum, I took the advice of replacing the head unit as the first step in upgrading (huge thanks, BTW). On a budget, I purchased an inexpensive Sony Xplod CDX-GT640UI ($149) after reading good reviews from it. All I can say is WOW! It does make a huge difference! I was even planning on buying new speakers later, but I will even hold off on that for a while. Also, before I dismissed the Subie OEM subwoofer as total crap, but now it has come to life!
Thanks again to the people in this forum for the good advice, and best wishes for 2010!