Guess I'll throw my two cents in.
1. Consider the Warranty:
The supposed AVERAGE life on an LCD screen is 5 years.
When the LCD screen goes bad, they are very difficult to fix. Outside the manufacturer's warranty (usually 1 year), you are looking at repairing or, worse yet, replacing the set out of pocket.
We bought an HD TV home theater system on special at Best Buy just before Thanksgiving. The package was all Sony (52” LCD + 120 watt home theater (w/ Blu-Ray) + a second Blu-Ray DVD player) for $1900. (There was also a parallel deal but with a Play Station 3 instead of the second Blu-Ray. But my kids are grown and I want nothing that might tempt them to come back for an extended stay.)
Bought the “no excuses, in-home servicing, three service calls and we replace it” extended warranty from Best Buy. Cost about $300 to get coverage through November 2013. With Sony quality, it might ultimately be a waste of money. But I'm watching the television for the next 4 years without worrying what to do (or how much it will cost me) if a problem develops.
In five years, it will be 3D HD (which will require buying new everything); then onto “smell-o-vision,” I guess.
2. Get a 1080P television with the highest cycle rate (120 or 240 hertz)
1080P is high definition picture resolution rate (as opposed to 720P which is standard definition). To me, watching 720P now makes me feel like I need a new prescription for my glasses. You've seen the difference in the showrooms. The higher hertz rate means the screen “refreshes” more quickly. This is important when watching fast paced sports or CGI-heavy action features in HD.
3. Upgrade Your DVD Player
Get a Blu-Ray DVD player along with your HD TV. (Hopefully in a package deal like the one I got. The 52” LCD television regular price essentially covered the cost of the home theater and 2nd Blu-Ray player.) Yes, Blu-Ray movies are $5.00 to $10.00 more expensive per movie in the stores. Instead, buy them on Amazon or from another on-line retailer at very reasonable prices. The difference in picture quality (especially the CGI heavy/animated features) is tremendous. In addition, for the basic $10.00 monthly subscription fee (3 movies at once), you can have access to literally thousands of Blu-Ray movies through Netflix.
BTW, all of your present DVDs can be played in a Blu-Ray DVD player as well. (That's a general statement; there are probably some oddball DVDs that won't. I have nearly 200 regular DVDs from major studios; so far, they all play fine.)
4. Upgrade Your Cable Box to HD.
I was paying for a cable package that included HD channels I could not access because I did not have an HD television AND an HD cable box. After the television was delivered and set up, I exchanged the box at the local office but still ended up having a technician come to the house when I couldn't get sound with the picture. Turned out to be a signal source selection issue (D’oh!). The HD box costs me an additional $3.00/month.
5. Afternoon light on the LCD screen.
Can't help you much here. From your description, we have a family room setup somewhat similar to yours; but our television wall is at 90 degrees to the big sliding doors. Haven't had any problem with sun glare so far but it is winter now and the sun's angle above the horizon changes going into summer.
Good luck!
Some comments:
1) I would consider an extended warranty, but the high price of these extended warranties are in many ways a ripoff.
2) The two models I'm now considering--Samsung LN40B650 and Sony KDL-40EX500--are both 40" 1080p panels with optional 120 Hz refresh rates. I will not settle for anything less.
3) Getting a Blu-ray player will probably be a few months down the road. I already have a Panasonic DVD-S35 DVD player with progressive scan output and will use that as a stop-gap measure until I get enough funds to switch over to a Blu-ray player (any suggestions for a reasonably-price model nowadays?).
4) I DEFINITELY will upgrade my cable box to HD! 
But it won't be the box provided by Comcast--it will be a TiVo DVR with a Comcast-provided mCard CableCARD so I can at least get the above-Channel 30 digital cable channels.
5) Alas, I look at the current TV in the early afternoon and with the shades closed, the brightness is fairly strong. That--alas--may rule out considering getting a Panasonic plasma panel anyway.
I got a very similar deal as you did, but I got mine from Sony Style. Luckily there’s a retailer here in my hometown, so I got the 52” XBR9 and got a PS3 for bluray and streaming movies, a new mid-to upper line 7.1 receiver and a FIVE year warranty.
Interestingly, I went to Best Buy during the buying process and layed out the same deal (I was asking them to match) but they wouldn’t match-and I wasn’t asking for a five yr warranty as I didn’t know the Sony factory extended warranty was an extra yr when I was dealing. I am extremely happy with the purchase. (They let me walk out over $149 on the package)