Ricred1,
I was wondering where you were in this process. I know how hard it can be to pull the trigger on such a large purchase. I also know how much harder it is when the item that you covet is at the top or even out of your price range. I wish you well with your quest.
I have had extensive listening sessions with w/p 7's but not direct side by side comparisons to the w/p 8. I found the w/p 8's to be smoother on the top end and a bigger bottom. I tend to listen to rock and pop recordings which are not always the best. The 8's definitely made these recordings more listenable.
I later upgraded to the the Sasha. Much better speaker. The Sasha IMO sound much more like a mini Maxx 3 than an improved w/p 8. So, in my experience, there is an improvement from the 7 to the 8's but it is more subtle. The improvements from the 8's to the Sasha, IMO, is quite significant.
Is it worth the extra money to go for the Sasha over the 8's? Only you can determine that. If your experience is like mine you will find that the 8's sound more like 7's and you will still lust for the Sasha's. :)