I came to the same conclusions with my own compiler from perl to C. Lot of work went into generating perfectly readable and formatted C code, with all the whistles and ifdef's for debugging, tracing, Config and architecture optimizations. The good thing is that it's much easier in the compiler to do than in the resulting C code. We generate a lot of C code now, automatically, for perfect hash tables, optimized unicode tables, generating API's and exhaustive test cases and much more. It must be pretty and usable, gambit-c is a good example for throwaway code nobody wants to debug or read through.
Indeed. If you want to support full Scheme semantics, with continuations and all the crazy control structures, you really need to contort the C language into a form that's pretty hard to grok. That's the sacrifice Gambit and Chicken made, and it's probably a worthy one given how excellent and complete those compilers are.
Pre-Scheme is intended for a different use case -- when you want the level of fine-grained control that C gives you but don't want to leave Lisp behind. Its semantics are accordingly quite different from Scheme's and it doesn't support the full set of Scheme control structures, nor implicit garbage collection.
