I have a 50" Panasonic Plasma and its great, like you found out they can be had for around $700 to $800 now. Things to remember about 720 and 1080, unless you use Bluray or something similar you won't be getting 1080 and past about 9 feet your eye can't see the difference in detail, so it makes little difference. The larger the size, the more you will be able see the difference up close though. Cable and satellite are 720.
Yes but 1080p is being implemented, I would NOT recommend 720 when 1080p will be the standard.
The refresh rate makes a huge difference to me and watching an LCD when there's a great deal of action on the screen can give me a headache quickly, so this eliminates LCD an option. I can see it even on the newer faster LCDs, If it wasn't for this it would almost be a tie between the two types.
I doubt you can see it on the 240hz refresh rate, as they handle motion and action BETTER than plasmas now, this is an old thing, just like burn in on plasmas.
Power consumption on a 720 plasma and any LCD is about the same, the 1080 plasmas use slightly more, but its not something to worry about. This testing was done by Consumer Reports because of all the buzz about it.
LED LCD uses less than 50% of the energy standard LCD uses, and much less than a plasma. Not sure what CR you are reading.
When in doubt go bigger, if there wasn't such huge price difference between 50"s and bigger when I bought mine I would have gone bigger. Consumer Reports listed buying too small of a TV as the most frequent regret.