I believe also it amounts to the same thing, since it conveys the same feelings:
Why would you thank in advance if you were not looking forward to sth and the other way round when you say you are looking forward to sth, often the required thanks are implicit or it's just your particular way of saying thank you !
In certain formal contexts you can say : " je m'en réjouis" as in:
A: -"je suis heureux"
B: -" je m'en réjouis" but I would rather say -" je suis content pour toi"