We're doing only the dictation with CTC, and I am really pleased with my ds's spelling, even within his own writing. His written narrations have only a few spelling errors, as well as his other writing. Spelling has always been a concern for me with my oldest ds because he was very premature and had speech therapy for several years. He had a harder time with spelling at first, but the CM Methods in HOD have really helped him blossom. We also did dictation only last year with PHFHG. The year before that with BHFHG, I did R & S Spelling along with the dictation and ended up dropping R & S Spelling halfway through the year because I thought there was little retention from it and no carryover into my ds's writing.

(On the day he passed his spelling "test" in R & S, he misspelled two of those exact words in his own writing in the next subject

I pointed out that he'd missed those words and he told me, "Yeah, I really don't remember these words after I'm done with them, mom." That was the day I dropped it).
I have been on this spelling journey you are on, and all I can say is my journey has led me to believe dictation is enough, and not only enough, but the best, most effective way to teach spelling in such a way that it is carried over into personal writing (which is really the goal of all spelling)

. I'd throw out a challenge to give dictation (following the procedure detailed in the HOD guides) a fair shake on its own for a year or two, and then add spelling back in if you think your dc still need it, but if you are feeling really torn about this, you can always add in some other spelling this year too.
In Christ,
Julie