Better fuel economy will be hard to do. You are moving a box. The 2-1/2 inch exhaust will add power and I would do it all the way back. You can get cast dual headers which will help also but make sure you still heat the intake for drivability especially in cold weather. A better flowing intake is a nice idea but you probably lose milage with bigger carb.
This sounds funny but anything you do will be for personal satisfaction. The cost of changes are usually never paid back in economy unless you keep something a long time and you are consistantly a driver who strives for fuel milage....Good Luck
