I've had the newest readers for the most part since the PRS-500 was introduced. When the 505 released, I sold the 500 and got it....spent a couple bucks more, but it was worth the upgrade. When the 700 was released, I had bought it, put the 505 up for sale and pulled it and returned it immediately as the screen was not to my liking. Then the 600 released, and I havent turned back.....
Point is I have been able to upgrade all my electronics at minimal costs because sales forums and Ebay is your friend
No need to wait for the next best thing, because the next best thing is always around the corner.