All we're seeing right now is manufacturers issuing remixes of the same basic package. The essential element in an ereader is the screen, that hasn't changed for a couple of years and any real improvements are still quite far away. The Apple Tablet will just be an LCD screen in a shiny case with some intensive marketing.
If you find a package that offers a feature that's really important to you (as multi-lingual dictionaries might be), then that might be a reason to switch, I suppose. But frankly, as others have said, the 505 represents the state of the art for ereaders, and will continue to do so for some time.