A few people have mentioned the rule clarifications and ammendments in the two D&D boargames that follow Ravenloft, and that these improve the game. I haven't had a look yet, but I'm sure they'll be available online somewhere - is there any reason they wouldn't be retroactive? I wouldn't mind some line of sight rules, since Ravenloft has none, and perhaps some clearer movement and figure placement rules.
The clearer figure placement rules are easy to retro-fit - the later 2 games state that monsters should be placed on the scorch-mark/bones square, not just when appearing but also when moving, except when their movement rules specifies otherwise
There's no line of sight rules, it's been super abstracted, so yeah sometimes monsters and heroes can appear to fire round corners, but that's how the game has been designed - simple & fast
I don't think there's much else in the new rules that would affect or could be fitted to Ravenloft.