A zoom would add a lot, IMHO. With the increased resolution, it would be a nice touch--not so much for tactical combat--but for searching, thieving, even just to get a closer look at your avatar's armor, etc. I've been playing a little IWD II recently, and think a feature like this would be useful and appreciated. For situations like walking your party around a town, you could zoom in and get a closer look at your immediate surroundings, instead of just looking at a screen full of rooftops. Same goes for a narrow dead-end tunnel, when the rest of the screen is black.
I have this sneaking suspicion that the zoom won't have quite the range you're expecting. The area pixmaps likely won't scale well, so there's no point in allowing zoom down to the point where you can see the armor details. My guess would be down to 2-4 × normal.
I would enjoy a 2x zoom, any more would be gravy.