For what it's worth, my very first efforts at translation hacking involved hand-assembled machine code. ^_^;
As a long-time programmer (however thin my actual resume might be), I can say this: game designers who can code have an advantage over game designers who can't. Generally speaking, it's faster and easier to make a game do what you want if you can write code as opposed to having to deal with premade behavior and action patterns.
The miracle of Stencyl, however, is that it narrows the gap between coders and non-coders. There are still things that simply can't be done using blocks, but practically all of the commonly-used API functions are represented through them: you can create fully-functional complex games without writing a single line of AS3.
The ridiculous thing? Even though I can code in AS3, I still use blocks when I can. They're more cumbersome than pure code, to be sure, but the fact remains that I can use 99% of Stencyl's advanced functionality without having to memorize the ins and outs of yet another API.
Stencyl's blocks are not a substitute for code; they are code. Stencyl users are becoming coders, whether they realize it or not. Once they learn the statements that correspond to all those colorful LEGO bricks, the transformation is complete - and yet I wouldn't blame them in the slightest if they kept using blocks, relying only on pure AS3 for the fiddlier bits.