You know this only because of Thomas's record AFTER he was confirmed to SCOTUS.
Thomas, IIRC, had practically no written record before his confirmation. Kinda like Miers, wouldn't you say?
(And btw, I too supported Thomas at the time, as I do Miers now -- at least until we get to hear her at the Senate confirmation hearings.)
Who's to say that Miers wouldn't build up just as impressive evidence of "wide-ranging, expansive mind, familiar with natural law theory and some of the big ideas that lie behind our constitution" -- during and after her confirmation, too?
It's extremely unlikely. Thomas had the background and made the most of it. Miers doesn't.
You are right on one point. Mostly I listened to Thomas talk, and was impressed with his obvious intelligence and breadth of understanding. I have read a fair amount of Miers's writing and looked at her record, and I don't find anything of the kind. Her natural mode is gushy and fuzzy.