One thing that I think is worth noting is that - though I like the PT (and love ROTS) that doesn't have the simple metaphorical or idiom stock value that the OT had, not even close.

-Darth Vader as shorthand for scary, all-powerful dude

-The Force as shorthand for religion/spirituality/wisdom

-Yoda/Obi-Wan as shorthand for wise old man

-Death Star as shorthand for weapon of the power structure

Even less common things, like Tattooine being cited as a backwater place from time to time.

In this sense, I think the OT is much like the Bible or popular folklore - like Robin Hood being shorthand for guy who steals from the rich to give to the poor. But the PT was just too complex and/or plain ol' messy (both in plot and characterization). As LFL has increasingly doubled-down on the PT direction of things - by making the TCW cartoon, customizing the OT to fit the PT in the BluRays, but not the other way around, releasing TPM 3D, etc. - they're really either trying to prop up their weak spot or else they just don't know what part of the movies truly resonate with people.

So I think that, because of their true comparison to the Bible and popular folklore, the OT will live on as long as anything in our culture. But I don't expect that people will often be citing, say, Nute Gunray as the shorthand for a corrupted, myopic businessman.

So it's all limited to the OT.