$300-$500 I'd say replace the Rockfords with those Stryke AV12s I linked you to. They are very nice and actually have the side benefit of looking spectacular too, as if that's even important. Like I said they are pretty much the best displacement you will get at your price point, and should be a noticeable improvement even with the same amp you're running right now. If you sell your old stuff use the cash to get a JBL 1200.1 amplifier to power them and you will have a marked improvement in SPL and in sound quality as well. It's a win-win situation.
If you decide to keep your current amp and run in a lower power class (uder 600W) I think you would have a chance to win some comps. I would also have a new box made for the AVs, and tune it specifically for the subs. Remember, no matter how good the subs are, you can destroy thier performance by using the wrong box, ar a poorly tuned ported box.
