Does Grease Cause This On A Kennedy Half?

Yes that is from a grease-filled die. Very common.

Not severe enough to have a premium.

How can you tell for sure. Note the bottom of the 'S' on Trust? See how it is wider there? The filling of the die prevents the narrow parts of the devices to form, leaving the wider part of the devices that present:

The more you read here, the more you will learn. Best way to learn is to look at the first post. If images are there, determine what you think you are seeing. Then read the other posts to see what others think. That way you can read at your own pace and learn more. I like to expand a subject so they will see what I see on their coins. Thus the reason my posts are longer than others. I try not to give yes or no answers, but explain what I see, so others can add that information to their knowledge.