Late last year I had a plasma, forget which model exacty but it was 42" and 720P, used it mainly for gaming and the occasional movie, and I too originally thought that there wasn't that big of a difference coming from dvd to blu-ray....Until I watched lost season 3....HOLY !!!! I honestly felt that I could reach out and grab what was on screen, the depth and realism of the image was incredible. I had seen it in HD on expressvu, but it didn't even come close to the blu-ray version. Since then there have been a few releases that have given me the same feeling, which I definitely do NOT get from dvd, regardless of the transfer. And after finally getting my HT kind of up and running I can agree with Tonyvdb above, the new lossless audio formats are something to behold if you're system is up to the task
*edit* I just re-read your post, and looked up that integra receiver, that's a nice piece of gear, I mean HDMI1.3 the whole nine. So if you've spent that kind of cash on both the display and the receiver why not do blu? You will hear a difference in the audio, the quality of the transfers are getting better and better...With the money invested, as well as the capabilities of the display, and the receiver I would grab a PS3, it's a software based player I believe which makes updates a heckuva lot easier, and it's kind of a flagship product for Sony so they keep it pretty up to date.