Well of course you could always use some additional stealth damage. However, given the already very large amount of damage that assassins perform, you may be better off focusing your buff on other things. I'm not too familiar with the shadow tree, but sometimes run a knife / assassin. With knives of course you'd be thinking about your RCT. Though as far as assassin / shadow, i'm not quite sure what your tactics would be with that loadout. I would suggest though some gear that'll buff your analyze weakness for a better chance of it working.
Thing is, that from what I understand, that concealment detection right now is broken......which sucks, but for an assassin that is a very large advantage, and allows you to focus your buffing on whatever areas you think are neccessary for your particular tactic.....ie, dr, vd.......maybe mct to try to finish off an opponent in IL (<--not terribly likely on that one though).