Just for a lark, I tried expanding the Himal interceptor's spins from 20 to 40 using Photoshop, and it came out pretty well. I don't think that this process would work as well for larger ships, since camera angle becomes a lot more evident and masking can become very complex, but on small ships the camera "stutter" isn't that noticeable.
For people interested in trying this, you can create a 40-spin graphic by rotating every spin frame by 9 degrees and interlacing the resulting frames; you can do the same with the mask (it may require some prodding since most imaging programs don't like rotating 2-color images) or use a "magic wand" tool. To have your mod recognize the 40-spin, just add rotationcount= "40" to the ShipClass tag.
If you're interested in seeing what 20-spin upconversion looks like, the Himal Interceptor player ship mod is at http://xelerus.unrealcrystal.com/index.php?s=mod&id=47
