Well, it's obviously going to depend on which TV you go for - I know the Panny's of late have not been as fantastic as those of old, but it's fairly understood that the bigger the TV, the easier it is to see the real difference between standard def and high def. Given this, yes, an upgrade in screen size will help, as should an upgrade to a Full HD screen, as opposed to an HD ready screen like the 37PX80B.
At the end of the day though, you really need to go demo these screens - it's what made my mind up.