I have a 52W3000 and I'm quite pleased with the way that it handles SD--however, it's highly dependent upon the actual source. Some SD channels just look plain bad, while others are pretty good. I blame this on the signal and not the TV. Generally, the digital channels look better than the analogue ones. One way to see how well the set can handle SD signals is to view a new-ish DVD movie on it. I think it looks very good. With SD, going to a larger size is not going to look as good especially from the same viewing distance as the smaller set. If you move farther away, the quality should improve.
I wouldn't worry about your manufacturing date as long as yours came in an unopened box. My set has a build date of Sep 07. From what I've learned there have been revisions (according to different firmware numbers) but no significantly noticeable way to tell what the difference is since the TV seems to function the same. In fact, I had to return my first set because it was defective. The replacement had different firmware, but the same build date. I couldn't tell the difference at all.