It's extremely funny that right now, I can buy missiles at my score (Just over 600) and be able to hit the top 3 nations in game and launch missiles at them, doing more damage to them that they could ever deal to me (Monetary wise)
What I propose is lowering the up scale war declaration range to within 150(As an example) points of your own score. So even if you decide to declare on a nation larger than yourself, it's not going to be too far out of your own score that you'll be doing loldamage with missiles against them.