Well, I’m all for simple models, as it makes the rest of the process easier, but if you are looking for ways to improve this character, modelling might be a good place to start. It wouldn’t have to be anything too extravagant, even if you just accentuated his bug-like characteristics by adding some creases, or spines, or more of a joint at his joints.
If you are absolutely finished with the modelling, (I know we all have to bite the bullet at some point) then texturing could take it a little farther. If you could spare the render time, then you could try a displacement map to make up where modelling left off. Give his skin a little more texture. Aside from that, I would vary his specularity and glossyness a bit more, maybe add a (subtle) bump map that coincides with the markings on him. As for the markings themself, are they totally procedural? It wouldn’t hurt to paint them by hand, or at least add a little more to it that doesn’t seem quite as computer generated. Try playing with color scemes a bit more, too. Especially his face. You could add some more saturated green or blue, to, say, his eyelids or something, just so that his whole body isn’t the same color. His feet shouldn’t look exactly like his head, is what I mean, because he walks with his feet, and talks with his head. So maybe his feet are a little dirtier, and his head tends to catch your attention. That part is for you to figure out. Try putting him in his natural enviorment (whatever you may imagine it to be) and then see how the color/form/texture compliments it.
Hope that helps.