If you ever tried cycling and moved from Aluminium Mountain Bikes to Aluminium Road Bikes, you would feel a very big difference in terms of distance and speed that you could generate.
Having said that, its not just how much weight you throw out, but where that weight is matters. If you are trying to reduce weight, give priority to the furthest from the center of gravity of your car. As you drive especially in stop and go traffic, your car will dip in front during braking and tend to load the rear wheels while accelerating. The engine has to develop enough torque to pull those far away masses. Repeat this for every time you pull up to traffic lights.
Race cars may want to relocate their batteries to the back for a balanced weight distribution in corners, but it does not do anything for fuel consumption. Since its a race car, they don't bother. The battery would be better close to your center of gravity. Ever notice why its located to the opposite side of where the driver sits? That's to offset the weight of the driver.
And if you wanted Ti or Alu bolts, try
http://www.torontocycles.com/Selling...num_Bolts.html Those that's in UK could try ProBolt who makes these for motorbikes
http://www.pro-bolt.com/ they are used to be called Tasty Nuts.