Well, there are gals going this route - my best friend (girl) is the Best (Wo)Man and she is wearing a black suit because she hates wearing dresses.
I, on the other hand, like wearing dresses. I also don’t object to a black pant-suit but I suspect it would have been quite a bit more expensive than the dress to get a nice one, and a black pant suit isn’t really good ‘party wear’ if I wanted to wear it at Christmas or New Years or whatever, whereas I think the dress could serve that purpose.
Very nice. The head piece is no biggie–a plastic comb, some feathers and silk flowers, maybe a little fabric, a good slap with the hot glue gun and a few stitches, and you’re done. There are lots of tutorials online if you Google “fascinator how to.” And if it still seems intimidating, there are plenty of crafty folks around here who are happy to help you.
Yah, my BIL is all arty and I’ve roped him into helping me I think. I agree a comb and some feathers is probably as kooky as I can get. 
Bonus points if you go for the birdcage veil! There’s an awesome-looking eHow on making birdcage veils. I kind of want a little hat with one just to wear around the house.
I vote for this. Dress up like waitress diner Aretha Franklin. Casual and comfortable.
There is nothing about that which says ‘semi-formal’. Like not even one thing.
In Southern California it could pass as semi-formal. 
You could just say that the Blues Brothers part was more important to you than the semi-formal part. Isn’t Aretha Franklin the Queen of Soul? If a Queen isn’t formal enough then I don’t know what is.
50’s style???
The Blues Brothers was set in 1980 Chicago.
Sure it was, but their outfits were NOT 1980s style, at all.
The only people in the movie that were dressing out of character for the period were Jake and Elwood. Everybody else in the pic were pretty true to late 70’s, early 80’s.
