Would it be a good idea to include an SVG version of the graphic?

Yes, for the reasons you wrote.

Shall the calculator screen contain the text GCC4TI? This would make sense on higher resolution levels, but should probably be left out on lower ones.

I agree.

Shouldn't the logo also include the 89 OS signing key at higher resolutions? (okay okay only joking)

On a related note, http://decss.zoy.org/ , http://www.cs.cmu.edu/~dst/DeCSS/Gallery/ and http://www.cs.nmsu.edu/~joshagam/css/ , though: it _is_ possible to distribute the keys in clever ways, some of which being such that TI would have a hard time persuading a court to consider them as DMCA violations...