It is possible that PMA 2007 will see an S4 IS. I wouldn't hold my breath, as the S3 IS is still relatively new and may be too new to be replaced yet.
Whatever you do, there'll always be a new camera around the corner, particularly in the compact market. The technology has got to the point where the upgrades between models are relatively small, but the marketplace (or, more likely, the dealers and marketers) are always demanding new models.
Even if an S4 IS does emerge at PMA 2007, it's not likely to have huge improvements over the S3 IS. SD HC support can, I think, be seen as certain - but this will only affect you if you take long movie clips. Anything else would only be a guess.
The way that I'd look upon it is that you don't have a working camera at the moment, which means you can't take pictures. The S3 IS does have some improvements over the S2 IS, and it seems worth the relatively modest extra cost over repairing your broken camera just to have a new unit and a year's warranty, especially as, for a compact camera, you use your unit heavily.
You could always eBay the broken S2 with the word "broken" clearly in the title of the auction and a clear description of the fault and the overall condition. Someone may give you a little bit for it, especially if they can take parts from your broken camera to fix their broken camera. Even if it's only a few dollars, that narrows the price gap to a new unit a little more. Just don't get sucked into any kind of scam to send the camera by insured carrier then participate in a scheme to claim that the camera was broken in transit.
David