After a year I couldn't be more happier with the Premium especially with KT-77 and Cifte tubes recommended by Kevin. The Premium with these tubes have a beautiful midrange and the best soundstage and holographic sound I ever had in the 40+ years of being an audiophile. I also replaced the Focals with Lawrence Violin SE speakers which sound wonderful with the Premium. The Focals with the beryllium tweeters were a bit too bright for my tastes.
So the answer to your questions, Was it worth the price difference, I would say yes. As to the improvement, was it large, no but there was a difference that I'm glad I made the purchase. Either PL dialogue integrated amps are a best buy in my book.
BTW- the icing on the cake was replacing the stock fuse with an Audio Horizons Platinum fuse. This fuse added another dimension to the sound that I was able to hear further into recording and more detail.