First of all, if you are going to spend the money for one of these displays, I believe you are setting yourself up for disappointment if you do not upgrade your subscription to include HD. In fact I think it is inevitable that you will do so, sooner than later. If that presents a budgetary dilemma for you, than I suggest you deal with it now, before you buy, or else delay the purchase until you can afford both.
While some flat panels do SD better than others, I have yet to see any flat panel display SD content anywhere near as competently as a decent CRT, regardless of brand. I would wager that this will gnaw at you every time you watch network or cable programming, knowing that HD content is available within minutes of a quick phone call or a few mouse clicks. If you like sports, once you watch an event in HD, you may find it difficult from that point on to watch the same thing in SD. I think the most common HD comment I hear at work is that they would rather watch something crappy in HD than something better in SD (while I do not subscribe to this mindset, among my family, neighbors and coworkers, I am clearly in the minority). At the very least, consider putting up an OTA antenna. I live near Chicago, where bad weather can make satellite reception unreliable, so I use an antenna as a backup for local channels. Actually, local channels look better via an antenna than a compressed satellite signal anyway.
I do not agree that using this forum predestines you to learning the hard way, or that you should absolutely not listen to anyone here. If that were the case, there would be no point in having the forum in the first place. I do agree that you will need to filter the responses and make your own decision based on your own research, shopping, viewing, and acquired knowledge. I suggest you try to find people who have these displays in their homes and see if you can watch them in that environment and lighting. Neither of these sets will display a picture that resembles what you saw in a store. There are plenty of good reasons to choose or reject either of these displays, and only you can decide what matters most to you. It's your money, you're the one who will watch and live with it. Don't let anyone else make your decision for you.
As to your 3 priorities:
1. SD content: IMO, SD only is a mistake. I recommend you reevaluate this plan. I think the Panasonic does a better job with SD, but IMO, neither model does SD very well.
2. Blu-ray: There are other factors such as lighting and viewing angles that may influence your choice, but depending on models, more often than not I generally prefer plasma for watching movies. In your case, based on the 2 models you've specified, I would choose the Panasonic over the Sony, based on black levels and motion rendition. Some say the Panny appears reddish; I did not notice this in the store, where the lighting and the settings are all wrong anyway, and neither set was being fed Blu-ray. Others here generally prefer LCD, and if that's what their eyes like the best, then regardless of their logic, they are just as right as myself or anyone else, because that's what looks best to them.
3. Gaming: You will see conflicting opinions and arguments from one end of the map to the other on this topic, based on motion blur, image retention, burn in, phosphor trails, color rendition, etc. Sorry, I am not a gamer, I have never viewed nor evaluated displays with gaming in mind, and cannot help you with this.