I think most of the underused stars could qualify for a "cruiserweight division", so for me that's the principal reason they're being underused.
That being said I also agree that Antonio Cesaro is the most underrated performer on the roster right now. Here you have a guy that can make anyone look good in the ring, that knows a lot of languages, that is decent to great on the mic and that has the physique of a credible champion and he's hovering on the roster, still looking for a place to be. Hell, he could be feuding with Sandow or going against ADR in a series of matches for the WHC, instead of being aligned with Jack Swagger (with Coulter I have no problem) and doing nothing at all.
I rather see him tag up with Kassius Ohno rather than Jack Swagger if they want him in the tag-team division, at least the two of them could rock the tag-team division. But other than that... push the damn guy and see where he can take you.