50" Panasonic Plasma Question

I am looking at either buying the TH-PZ80U brand new for $1500 or getting a slightly used TH-PZ700U (last year's model) for $1150. Aside from the contrast ratio (20,000:1 v. 5,000:1) and an input for my PC (which I would rarely use) I can see no differences. My questions..

1. How much difference will that contrast ratio make?
2. Which is the better deal?

I have the PZ700U and use the HDMI for my Mac mini. The VGA connections resolution was not high enough for me.