On Windows it works ... until I try using --export-area. Whenever I give --export-area parameter, inkscape silently does nothing.
I pretty sure the problem is that you are using build of inkscape the is compiled as a GUI app not a console app.
Well, I am just using 0.45.1 downloaded from the website...
But your diagnosis seems a bit strange to me. Something like
inkscape --export-png destfile.png --export-width 80 --export-height 80 source.svg
*works*. So the general mechanism is OK. Only after I add --export-area it stops working.
(well, there are some small quirks - if I give bad file name there is no error message, just no result, I also had some problems with accessing files from different drive, but those are not crucial here)
I suspect sth stupid - for example maybe I should use something different than : to separate numbers.?