I think it all depends on the kind of group you have.
I'd only advise u to wear fancier clothes when teaching Business.
However, it is always a great idea to surprise your students.
I read a book a long time ago called "Breaking the rules" - can't remeber the author now - He said it is always nice to break the rules of the classroom, especially the teacher. For example if you always wear shirt and jeans, one day you could just show up wearing something totally different. I did this many times before and it worked pretty well!
