For me, fashion is also art. It may be subjective and it's beauty is in the eyes of its beholder hehe. And of course there are several other factors to consider in a musician's performance like stage presence, musicality (of course), etc...
If you're a professional musician who is making money out of your music, you should look presentable, now when i say presentable, i'd say wear something that is different from your "pambahay", or "pang-malling" clothes or what not. Good example would be showbands playing locally and abroad. They can't wear something similar to their "pambahay" nakakahiya naman yun hehe.
But if you're the simple hobbyist who's playing for fun, attire isn't an issue. Do whatever you want. But then again, if you're a pro, wear something nice.
Fashion statements need not be very bongga. It must match your individual style as well as your group's music. Sandwich is a good example, simple clothing but unique.
In fashion as well as music, i guess simplicity is still beauty.
For pros, fashion must at be least 20% of your musical artistry.
For non-pros, then do what you want.
Peace!