I'm not sure about King's Quest, but Space Quest certainly didn't have any concept art. Scott Murphy talked at length about his "flying by the seat of your pants" design philosophy. He just made stuff up as he went along. And for SQ1 particularly, he and Mark put together some rooms in a space ship with a space character and showed it to Ken who then immediately approved the game. But they didn't even have a game at the time, just a few rooms. The space ship turned out to be the Arcada sequence at the beginning of SQ1.
I doubt there was any real concept artwork going on at Sierra until the SCI0 (EGA w/mouse & sound card support) days.
Originally Posted by TomPravetz
This is the internet and you made a typo. Therefore, I won this argument. My opinion is now fact.