Firstly, the incoming missiles are not necessarily carrying nuclear war head. More likely the first batch comes will be those with conventional warhead which is aiming to the BMD system;
Secondly, each missile will be able carry at least 2 heavy decoys;
Thirdly, unlike BM, BMD is heavily relying on complicated detecting, tracking system, etc, these systems are not only expensive but also vulnerable.
Read my post carefully!
Both in terms of individual missile cost & the "program" cost, Nuclear/BM program easily trumps BMD.
Also, you just made up all that stuff in your post - it doesn't belong to any countries' strike doctrine!
First "batch" of BM's are duds? Did you even think through the logic before you posted? You just negated all the advantages of a first strike!
Once a barrage of BMs are launched towards opposite territory there will be an instant 'nuclear' retaliation. Because the receiving end would counter-launch nuclear missiles either suspecting the incoming BMs to be nuclear tipped or knowing that you're the smart general whose second barrage will be nuclear tipped BMs!
Your strategy is like pulling the trigger on an unloaded gun with the hope that your enemy will exhaust all his bullets firing at your bullet proof vest! Once they see your (empty) gun, your head will be blown before you attempt to load your gun!
You either take the first shot or be dead for the stupidity of brandishing an empty gun!
Also, countries like Pakistan will have only a handful of BMs(that won't be wasted in a foolish gamble). while there won't be a dearth of cheap BMD missiles (eventually) with India (which are smaller & produced in large quantities)!
You should do some research on how much a country spends on their entire nuclear & BM program; compare that with the budget for BMD program and then comment. Typing by the seat of your pants is not beneficial to the forum.