It probably does sound better but not with the ears I've got
(I don't have Sky i'm afraid I use FreeSat)
Some folks have had issues with the Panny stuff on here but my experiences have all been good. Vieralink or I think its now "Smart Viera" is just a proprietry Panasonic set up to allow control and intergration of your devices usually all done through the HDMI leads.
I have a Panny tv and home cinema and they can be controlled by either remote for most things. It may save you having to make an additional physical connection or two.
In so far as HD vs standard, if you are going up to a 37' LCD/Plasma or above you will see a big difference in picture quality on HD. If your old tv was a normal CRT of say 32' the picture probably looks pretty sharp on "normal TV" but when you expand that picture up to 42' say it can look a little washed out hence the move up to HD.
I still haven't gone to Blu Ray yet but have a Panasonic upscaling DVD player which works great (although my eyesight is starting to follow my hearing)
I understand your problems there is so much information out there it's bewildering. I just set a budget and stuck to it. The main reason I went to Panasonic was for the 5 year warranty on the TV and the richness of the picture. If you buy additional shop warranty be careful that this covers the screen as quite often it doesn't!
Good luck!