Thanks, that helps.
So, the back and forth between raster and vector is indeed fairly massive, but that's because traditional approaches in the raster seem too slow (150 pixel windows are quite slow, that's true), you want to experiment using geometry.
Let's see what you can do right now:
You can convert a raster into a drawing - that's a simple query. (See TileToValues functions, say if you want an example query.)
You can then analyze that drawing using transforms in 9. Or using a script.
You can also export the drawing to, say, SHP, or perhaps export the table to CSV with X-Y-Z values, and process that data in other software, then import the result back into 9.
After you have the result, if it is just pixels and the pixels are still in their integer positions with just the values changed, it is fairly simple to put them back into a raster using a script. Again, say if you want example code.
If the result is areas or lines, then perhaps wait until we do vector to raster as a built-in tool.
PS: Request for degrees or percentages in slopes noted - I'll bump the wishlist item.