Hi everybody, coming back to the furniture plastic topic, let me tell you my point of view, trying to provide some light:
I owned an Spanish Advanced Quest version of HeroQuest some years ago. This version was titled in Spanish as "HeroQuest, EdiciĆ³n Renovada y Ampliada" which roughly means in English "HeroQuest, Extended & Renovated Edition".
At that time, I remember me comparing the plastic parts of the Advanced Quest furniture with the original game ones, which I still own, and I remember to study their differences. Honestly, I prefer the original ones due to they where the ones I owned when I was a child and because they appeared to be more solid or stronger than the Advanced ones BUT, I remember one good detail about the Advanced furniture plastic parts: They fit better with the cardboard parts than the originals.
Then, I don't think that the plastic design and moulding changes of the Advanced furniture were mainly motivated by production costings, maybe yes, but attending to the title in Spanish of the Advanced Quest edition, which suggests that this edition intended to renovate the original one, and how well its furniture plastic parts fit with the cardboard ones, those changes seems to have been also (or only) implemented as a product design improvement.
In addition, I also remember that miniatures were also different between both versions. Some examples: I remember that mummies where a little bit taller in Advanced than original mummies, chaos warlock is more inclinated in backwards direction than original one and also has a little blind hole at the back of the helmet, Gargoyle whip is slightly shorter, skeletons relative position to their base is also modified between both versions, etc. And, in general, all of the Advanced Quest ones seem to have more sculpt definition too than the originals and better positions at their bases which I think that contribute to reduce clashes with adjacent miniatures in the board.
Therefore, if my memory works well (please, could anybody check if my different feelings about cardboard fit between versions are correct?), in my opinion I think all those minor design changes had a combined motivation, not only cost-reducing.
I hope these words have been useful