whether something is worth the price (or otherwise) is really depend on your visual acuity, your budget and you persoinal caring (or not).
For example, my dad can clearly see the difference between 9G and 8G Pio and 800u in my house although they are not in the same room. His choice for his house AFTER seeing all that? Sony XBR5! Why? Although he can see the difference, he doesn't care about picture quality so making paying for anything beyond the XBR price (close-out pricing at the time, making it cheaper than 800u) is not worth the money.
Me? it's a different story. The differences are too big for my level of acceptability yet I don't have the money to buy another Pioneer plasma, so I sold my 800u and have the 3rd room only using my old 20" Toshiba CRT TV.
Beyond all that, regardless how "clear" a protective glass is, refraction will always be there. It's just simple physics. The further away the protective glass from the light source (ie, the plasma screen itself), the blurrier/hazier the resulting image will get.
I encounter this during my time consulting for commercial theatres and currently in my photography. Even when the manufacturer claim the material to have "zero" effect.
Tu push things further, take a picture with and without lens filter (even if your lens filter is a B+W filter costing close to $200 for a 82mm diameter) You WILL see the difference.
I'm pretty sure that Panasonic does NOT use a $200-grade for 82mm of diameter for their 50" TVs.
Regardless, I do admit and strongly agree that the Pana 800U is a kick butt TV for the money and suitable for most of the population. Just not the best and there many people like me looking and won't settle for less than the best either because of visual acuity or sometimes just because of snobbery.