I was very impressed today. I wound up doing the same mission two times in a row while exploring. Yet, because the nebula looked drastically different, the aliens I was hailing were drastically different, the response from scanning the ships was different and the conclusion of the mission was different, it didn't feel the same.
Now, if I do 100 of these missions, maybe I will have a different tune. And it would be nice if there was some way to not do the same 'base' mission twice in a row while exploring. But that might be hard to implement. Over all, I was pleasantly surprised with how different the same mission felt.