SDI is pure luck, but it is a part of the game that must be dealt with and planned around when doing target lists.
MP is needed, just look at last round. TEPD utterly destroyed Roman Empire and Skaro during our first war, neither alliance had nations in the top 5% (or very little) until very late into the round. If they didn't have access to an MP, they would be at a great disadvantage to anyone that didn't get hurt as bad first war or that didn't even fight a first war at all. With that said, people would be inclined to large downdeclares to save pixels or not declaring war at all to be able to stay within nuclear buying range.