Hi P.!
How fun! How about (either real or fake) record albums all over the walls? All sizes, 45, 78? is that right? LOL! How about cheap "ked-typed" canvas shoes that everyone can make into saddle shoes? (Some ideas might be too expensive but I'll throw em' out anyway!) There are decorations called "Scene setters or room setters" (Oriental Trading is one source that carrys them as well as Ebay) I don't know if they have a 50's sock hop but they're like a huge piece of wallpaper that changes the room. Even if you only did one wall you could make that a focal point. Have everyone dress like they were in the 50's (costume shops, thrift stores, mom & dad's closet!) and take black and white pictures. Some guys can be "greasers", while others preppy. Have the soundtrack of Grease play in the background or have several 50's groups play on a CD player with multiple disc changer that can play all night. Google "50's Party Theme" and see what others have done. I hope this helps.....
J.
p.s. ~Now do you have any ideas for a DIFFERENT baby shower theme with no gender? I was thinking baby blocks......Good Luck!