Unless you have a big collection of mono records, I'd probably hold off on the mono cart. A cheaper investment to hold you over would be a mono switch box, and even then I'd only get one if you have a decent number of mono records.
RE: the stereo cartridge, what is the rest of your system? You might be better off putting the money towards other components (e.g. speakers) rather than spending it on a minor cartridge upgrade. I assume the stylus on the 95E is new? If not, time to buy a new one if you have no idea how many hours are on it.