Very much agreed that captions are handy, whether you're trying to lean a language, actors are using non-standard dialects, you just didn't catch the phrase, etc. I think though, that for subbers to, not only make English subs, but also transcribe Korean subs is at least doubling their work. People don't have that much free time .-.
Anywho, I did a little search, and came across this blog. Maybe you or someone else will find something on the page helpful?
(Btw, so SBS's VOD site also has some select dramas available with transcripts... And while I believe Viki is about user-generated subs, maybe someone could y'know reference said transcripts and add some more Korean subs to the site. Or something.)