Unless you buy the special 4-hole Speedplay shoes or spend a large sum of money for the titanium axles, the weight is a wash. My Ultegra 6800 pedals with cleats and all hardware weigh 330 grams. A Zero Chromoly pair with 3-hole hardware weighs 334 grams according to Speedplay. 4-hole is down to 286 grams.
Cost per year to operate is very much in Shimano's favor. You could get back a lot of weight savings working a few extra hours instead of maintaining your Speedplay pedals (or buying new cleats) and purchase some weight weenies parts for your bike with the earnings
