D&D assumes a certain amount of magical treasure, which increases with character level. Do you think the assumed wealth level is appropriate for a Ravenloft campaign? In other words, do you think that a proliferation of magic items dulls the "gothic horror" feel of Ravenloft?
If so, why? And how would you recommend limiting treasure?
No, the magic items and magic don't "dull" the gothic horror, or at least, they don't have to if done the right way.
Saying Ravenloft ought to be low magic assumes, I think, that there is a certain amount of magic which would destroy the feel of Ravenloft, this "gothic horror" you refer to.
I think that, if it's done the wrong way, with magic that constantly serves as some sort of
deus ex machina device in the game, it does affect the horror feel of the a game. But it doesn't have to be done the wrong way.
There is a right way to run a game of Ravenloft, and for me, one of the specificities of Ravenloft is not only to be "gothic horror", but to be "gothic horror D&D". That's the fundamental difference between the boxed set and the S&S version, I think. The former sets D&D in a gothic horror environment, while the other fleshes out a gothic horror environment while not embracing D&D's feel.
Magic items can be perverted. Spells can become unsafe, awry, living creatures of their own. There are multiple ways in which you can make magic terrifying, make magic participate to the feel of gothic horror in Ravenloft. Taking away the magic of D&D altogether, however, would only make Ravenloft a standard, unoriginal, cliche'd gothic horror setting.