Yeah going from matte black to gloss black would seem like an awful lot of work for not much payoff. Whenever i've painted a bike it was to go to a drastically different color. If i were to repaint my satin red mtb, i would go to like a gloss blue, black, or green, maybe some awesome 80's neon splattering.
but to just change the finish seems like a major PITA for a minor difference in look. perhaps just touch it up with some black paint (scratches, wear spots) and then hit it with a gloss clear coat, mostly the same effect methinks.