Install ssconvert (part of gnumeric) on a server without GNOME
I think many of the dependencies for gnumeric are actually "recommended" packages, not real dependencies. Try this:
sudo apt-get install --no-install-recommends gnumeric
For me, this installed about 37MB of packages, most of which were libraries and icon themes, which I felt was tolerable.
I just installed gnumerics on my Ubuntu server : it installs a lot of dependancies, such as gnome and others, which seems heavy, but you don't need to load the desktop environment to use ssconvert.
My advice is : simply install it, don't care about gnome and desktops.