If you're thinking of say an AIM-120: it is always going to be helpful to be less visible to all sorts of sensors; in the launching aircraft, in other aircraft on the datalink, in addition to the built in radar when the missile goes pitbull.

If the opponent has less accurate data when compared to the less-stealthy situation; then the opponent will have a harder time guiding their weapons compared to the less-stealthy situation. It may also be easier to spoof, dodge, and/or hide.

Modern missile systems are getting smarter and smarter no matter what, you may need to stack several advantages in order to defeat them.