bombers ARE powerful, not just because they can move so far, but because you can use them so many different ways. They are probably overpowered for $12, but changing them threatens to make the game more difficult to win by nerfing a critical tool that the big teams need.
strategic bombing does influence the game, it is difficult to use against the Axis since Germany has a lot of production squares and Japan is hard to reach. Against the Allies, it is the only clear way to suffocate USSR UK-P and UK-home. Without the constriction of SBR, the game can be difficult to bring to a conclusion.
There are other ways to modify the SBR, which we have discussed at great length. However the core rules seem to be the best balance between offense and defense, changing the rules too much either makes it even more overpowered or not worth doing. If you feel SBR is too powerful, I suggest you reduce the bonus to +1.
KJF = Kill Japan First. This is usually 80%+ US commit of all $$ throughout the game. Attacking Japan sea+air across the pacific, it is very difficult to gain the advantage for the US unless Japan screws up. The only opening will come if he takes his fleet past SZ 37 to grab the $$, then you will outnumber him for 1-3 turns up north.