I've seen old G11 look good after a few years.
Not without resoldering the frame timebase IC on a regular basis you didn't

That aside, I've also seen a trinitron screen last way beyond what it should,
Trinitron tubes were way ahead of their time in the grand scheme of things.
I really do hope your plasma lasts as long as you hope.
I'm a bit of a gadget freak, so I have a tendancy to sell on long before the so called life expectancy comes about.
But back to the matter in hand, LCD is superior in virtually all aspects, for home use there is no reason to ever pick plasma now.
I can only speak from first hand experience.
We had the LCD, and all we got from that (aside from numerous breakdowns) was artifacts (pixelation) on dark scenes, shadowing between scenes, no such thing as true black (caused by backlight) and noticable (to me anyway) lag in fast moving imagery.
We now have the Plasma, and don't see any of the above.
Both sets are LG, and both got the best write ups for their class (so it's not like I originally bought $hit and then improved).
As I said elsewhere, what looks (or sounds) good to one won't necessarily look (or sound) good to another.....horses for courses.