Fox,
I was in the same conundrum. I had(still have) a 9 year old Sony STR-DB930 receiver. It still worked great. But as I have a new Playstation 3 for Blu-ray and DVD viewing, it (the Sony) would not support HDMI or the latest codecs.
You could do the cost/benefit analysis. Or, as AcuDefTechGuy has sugested, you could just say "look it's been x years. I want a new receiver dammit!"
I bought a new Onkyo TX-NR905 in June (and saved about $600 off full retail). I'm very happy with my Onkyo. No it did not blow up. It does run warm, but will not defrost frozen chicken! LOL
If you're considering a new receiver <$500, look at Yamaha and Onkyo. Denon's are great, but you'll probably have to spend hundreds more $ to get the same feature set as the lower priced competition.