I'm no expert but the plasma should offer a much better picture if viewed off center compared to your projection TV. I purchased a Pioneer a year and a half ago, just before pioneer quit making tvs. They made some of the best plasma's on the market. I don,t recall the model now, but a Panasonic Viera would have been my second choice, they make a very good plasma as well.
If I had the money I would buy a LED TV, they are still a bit pricey, but the picture is amazing.
View your current tv at all seating positions in your room them go look at the panny and decide if its worth upgrading.
One of the best upgrades I did was get rid of my Bose surround system and go with a Denon receiver and SVS speakers and a 12 inch sub woofer. The blu-rays came alive. SVS is made in Ohio and great quality at a good price. http://www.svsound.com/