Yes, a small weight savings, but look WHERE you are saving the weight. The weight of the casting at the top of the mast to support the block up there (the A Class masts just have a foam plug at the top of the mast and something for the ring to hook onto), the halyard all along the mast, and a block at the bottom. The most important place to save weight is aloft...and the support structure at the top of the mast for that halyard is a good place to save weight, even if you have to add it back to the plaform to meet minimum weight.

In cars, we used to say that it was worth it to pay $1/lb. saved, $10/lb. saved of unsprung mass, and $100/lb. for reciprocating mass. In sailing, think of weight aloft as the place you want to spend the most for weight savings. Lighter weight sail materials is always good, sometimes at the expense of durability. A lot depends on how much you sail and how often you buy a new Mainsail.