After the post ROTJ Ewok movie dirge SW started back on an upwards climb in popularity thanks to the all novels, all the Lucasarts games and all the toys from Kenner and Galoob. The PT may be the zenith of that journey but I think the OT movies would be remembered all the same without them.
But how much did the novels really help the popularity? I think that only die-hard fans were the ones reading the novels. I guess it depends how we measure popularity - to mean it means the spreading of the ideas to people who were not originally familiar with them. I don’t see how more content being consumed by the original base makes it more popular? No?