Starting out reading this thread I right away was aware of the problem with non-uniform scaling. However, I actually would introduce a "Font Width" spinbutton for fonts.
If you mean by this a way to scale letters non-uniformly without scaling the entire text object, then unfortunately SVG does not allow this. You can shift and rotate letters separately but not transform them arbitrarily. It's one the the gripes of mine. Maybe in a future SVG version.
concerning the scaling in height, I do suggest to _not_ show the new size but also have spinbutton for this showing the percentage of the original height. A button "set as 100%" for height and width will then adjust the font-size according to the skewed/streched width or the height respectively. I think this way all needs are served ;)
I'm not sure what is to be considered the "original height" here. In any case, you can work in the "preserve" mode and then you can return to the original point size by removing the transform= (though I'm not sure why this might be needed).
Anyway, the code for transforms changing point size (in "optimize" mode only) is now in CVS, please test it thoroughly (there may be surprises, as this is a pretty low-level change). The new code also optimizes the translation part of the transform into a change of x/y attributes on text.