I would hire a gourmet chef for the day and have him create signature dishes that are simple and easy to make. Have him slash your menu and limit the number of items offered. Likely he knows what people want and what can be prepared fast. After you are a raving success, you can add back in the menu items that have been dragging you down. But you might not, if you are smart.
Fast and unique food will be your marketing. With this method 100% will go to increasing sales for the life of your cafe. The other methods will get you 3% results for a couple weeks.