I know how to set the graphics options using the supplied tool. My question is, what combination does it take to enlarge the *viewable* area on the screen, so I can see more of the map as I walk. Right now the game is almost claustrophobically tight. I've seen screenshots on the WSG wiki that shows it can be done, but I haven't found a combination of renderer and scaler that works yet.

The only way I know of is to use Exult. If there's another way then hopefully someone can tell you.

Ah. Well poop. Alright then. Thanks!

In my experience the game runs better in Exult then in DOSBox, so that is recommended anyway.
You can't change the viewable area in the vanilla GOG version, as that was not possible in the DOS version and the GOG graphic tool only lets you change the DOSBox scaler/renderer settings. And these are basicly applied to the output of the game, so they can't change how much the game displays.