One quick way to see your height ranges in Wilbur is to use Window>>Histogram. It will show you how many of each altitude are present in the image.

With the ranges that you're showing and using replace as the operation, it was definitely just losing detail as it set the altitude to zero.

Adjusting the number of pixels in an image in Wilbur can be done with Surface>>Resample>>Simple. Why Resample instead of scale? It's a long and ugly story having to do with Wilbur's history, but resampling is changing the number of pixels in the image, while the Scale filter adjusts the magnitude of the altitudes. The Span filter is for those too lazy to do math: it finds the existing minimum and maximum values of the surface, then applies a linear scale to remap that range to the one specified.