Panasonic + plasma > > > > > > > > > > > Proscan + LCD
I'm not really sure why you think it would be a worse picture. It's the best picture for the size and money, unless you need something bigger and then I might recommend rptv. Unless you're closer than 8 feet to the TV or use it as your computer monitor, then 720p won't be an issue.
Edit: At 10-12 feet 50" is kind of small. Obviously it's bigger than 40", but since you're upgrading you might try to find a good deal on a large rptv. And 720p on a 50" TV definitely won't be an issue at that distance.
Someone on a deals forum said they just bought
this 60" DLP at HHGregg for $792 (not sure if that's before or after tax). That would be a much better size at your viewing distance. If you could decrease your viewing distance to 8-9 feet, then that would make a huge difference for the 50" plasma (however with the DLP being 1080P, you could sit that close to it even thought it's a 60"). Use
http://tvcalculator.com/ to compare different screen sizes.