I added a display for frames/second (fps), and discovered that my multi-touch version runs at about 13fps, so lower than I guessed by eye. That means the HD version must be at about 5fps. I decided to do some subjective profiling by turning on and off various features (such as drawing only the ripples, turning off sound, etc.) to find out what the performance hog is. Of course it's the ripple effect. Nothing else makes a huge difference, basically everything else drops the rate by about 3fps total.
So I tried changing the resolution to 256x150 (1/4 screen res), and poof, we got 30fps. The ripple effect is a little grainy, but I think with everything else at full res it might not look too bad. I'd rather have a smooth, fun game than a choppy, nice-looking game any day. If RIM ever decides to improve the performance of the flash runtime I can bump the resolution back up. I also tried 384x225, but that was about 20fps. And I tried changing the resolution of just the ripple map (behind-the-scenes calculations) and that helped, but the 256x150 combo was the only setting that got 30fps.
So now I'll be updating all the graphics to work well at this new resolution.