With MI2:SE they had learned from MI1:SE and made more or less everything right.
e.g. MI1:SE lacked voices in classic mode, no commentary, no achievements.
Since I prefer classic graphics I didn’t really care about the new one graphics except for curiosity (i.e. I’ve looked at every room in this new mode).
We all play the Ultimate Editions anyway, right?
Regarding MI3:
When creating a Special Edition we would have to add a classic mode, isn’t the current one already HD? 
But I agree with @pygy that scaling the actors like in TWP wouldn’t be that bad.
Another problem with MI3 for a proper remaster is the same they had with Full Throttle and Grim Fandango: Since it doesn’t use the classic verb interface the screen ratio would be off a lot, needing additional art to be created.