The Silhouette software has a vectorising feature from a scanned image. But, if you look at Eric's Spirit of St Louis thread, you will see that you have sometimes to rework the vectorised drawing to refine it, especially if you start from smaller-scale drawings or decals, that you enlarge to 1/32.
The Silhouette software is pretty intuitive to use, and I guess the most proficient among us could participate in a "Tips and Tricks" thread
I have not used the Silhouette software but I assume it is similar to Illustrator's trace image function. It does a reasonable job of turning an image into a vector but there's always clean-up and tweaking of nodes to do. I find more often than not, there are far more nodes generated by the software than is necessary. Particularly when it comes to letters.