Here's my current set up:

Toshiba 32" Flat Screen TV (not HD)]
Yamaha floor speakers (paid $300 for the pair)
Yamaha center channel (paid about $150)
Sony 5.1 Receiver (paid about 250 3-4 years ago)

Everything was purchased at Best Buy. I'm thinking now might be a good time to upgrade my receiver. How much bang for my buck can I get if I'm looking to spend $350-$500 on a new receiver? Is the upgrade worth it, or should I wait until I have more $$$ to invest. You'll notice I don't have rear speakers, but I am planning to add those soon. Would I be better off purchasing a new receiver first, or new speakers?

Thanks guys!

w