I think that soldiers should stay dead if they die in the street, perhaps less money for them but they dont resawn.
Also I have discovered a pathetically easy way to defeat every level, and survive up past level 70.
Just place nothing but soldiers down, in rows, first row rifle men, second row snipers..... until you have filled the map, then begin upgrading at strategic locations.
My above mentioned suggestion of soldiers dying for good would remidy this.
Otherwise, very well done and quite challenging, looking forward to future updates.
Thanks for the fun times.