I'm not sure that is evidence. SierraOriginals versions, like the one in the Yahoo auction, of games that had disk and CD versions are quite often the disk version on CD (this doesn't apply to later games, like KQ6, LSL6 etc).
On Dr. Brain, a Wiki SCI page says: Castle of Dr. Brain (CD version (if it actually differs))
It also says that for LSL1VGA on CD, which as I know is purely the disks on CD.
Maybe a rerelease did happen, but it was nothing to get excited about. I'm sure it was never talkie or enhanced. I've spoken to Corey Cole about it before, and although he never mentioned CD versions, he did indicate that after the game was made, he didn't care so much about Dr. Brain after that, largely because Sierra gave it to someone else.
UPDATE: http://www.amazon.com/Castle-Dr-Brain-S ... B000GI5KHO
It's a SierraOriginals release, so as far as I'm concerned, there was never a CD version, just a rerelease.
- Spike