Picked up a 60 inch PA6550 from Costco 4 years ago and it's still going strong, even after doing voltage pot tweaks for improved blacks.
Just recently, I was able to pick up a barely used Panasonic S60 on Craigslist, still had the stickers on them and everything. The S60 was known for its crazy black levels for the price, having blacks close to Panasonic's flagships that year for a fraction of the cost.
Just out of curiosity, I wanted to see how the tweaked LG's black levels compared to the S60's, expecting the Panasonic to blow the LG away. I used an HDMI output splitter and put them next to each other in a dark room. Used Samsara's dark city scene and Sin City and was actually really surprised that the LG not only easily kept up but almost seemed darker in some scenes to my naked eye. Wow.
The tweaked LG already had deeper blacks than my Samsung 60PNE530 (which was the non-3D, non-smart version of the PN550 of 2012), but I was shocked to see its black levels on par with a 2013 Panasonic.
Still wish they made plasmas.