Selling a GTX 570 to upgrade to a GTX 580 doesn't make a whole lot of sense, in my opinion; the bump in performance might not be all that great. Simply on that alone, I'd recommend waiting. In other situations with someone upgrading from something vastly older & weaker, (say, a GTX 260) I might have been inclined to suggest against waiting, but in this case it's probably the only way you're going to see a really appreciable difference.
While there's no clear word on when Kepler's going to finally hit shelves, and make whatever market splash it will, when it does, given the unprecedented high MSRPs of AMD's 7000 series, we'll likely see some forces driving prices downward. $550US is hard to justify for a card that isn't the #1 single-GPU part, and that crown is likely to be yanked from the 7970 whenever the GTX 680 finally arrives. The $450US MSRP for the 7950 already suggests AMD's prepared for some moves, and this in turn will likely spill down to affect the pricing of whatever 500-series cards remain.
If $1,000US is your limit, by that time, it may just make the most sense to wait for and get a Kepler video card.
As I recall the quiet part was how the suit was dropped for having little/no merit. (also, that wouldn't be an antitrust suit, it'd be an anti-cartel suit) The plaintiffs were pretty vocal about it at the time being, including trying to sign on a lot of co-plaintiffs, promising new GPUs and/or $50US+ vouchers that never materialized.