I like both players, but when you consider what you'd have to give up to get either, and how our roster is already formed, I'm not sure they're worth it.
For Mirotic, Morris would likely have to be included with Rozier and Yabu. I think Morris is a better player in the modern NBA by himself, but when you have to give up a starting quality guard and a prospect too, that's way too much.
For Randle you could probably do Rozier and Yabu, but then you are giving up your backup point guard with a prospect for a player that would probably be your 4th-5th big man (after Horford, Morris, and Baynes). He offers rebounding, but that's not a weakness of this team anymore. He can pass, but he commits just as many turnovers as assists. He can't stretch the floor or protect the rim. He might be a frenetic defender, but he is not a fundamentally sound defender. At that point, isn't Theis (and maybe Williams) a better option for our team.
The grass is always greener on the other side. Our team is pretty good.