I think I can best answer this using an analogy from English. Consider the following two sentences, both with "to me." (1) She is pretty to me. (2) She is useful to me. It should be immediately obviously that (1) expresses and opinion, but (2) states a fact. (1) is equivalent to saying "in my opinion, she is pretty." On the other hand, (2) is not an opinion - we don't read it as "in my opinion, she is useful." Rather, we understand the sentence as "she is useful" and "I am the person to whom she is useful." Likewise, in Japanese, the first sentence expresses an opinion because there is no set phrase "to be pretty to." The second sentence, however, is a set phrase where "ni" is the indirect object marker. XがYにもったいない, so it is not the same construction as the first sentence. I hope this helped!

I think is like this (but i could be wrong too) 1.- To me, you are very beautiful (Instead of "in my opinion" just "to me") 2.- For him, she is too good / She is too good for him には if I remember correctly more than "In my opinion" is "for (in regard of)" so it could be: to me, for you, for him/her And for the difference between the two I think they´re the same