I don't think I'd spend much money on trying to lighten a bike that's inherently heavy. As the other post said, 30 pounds isn't that badfor an all around commuter/beater/everyday bike, and you can sink a lot into it without making a very big difference. I commute on an old steel Bridgestone mountain bike that probably weighs 30 pounds or so, and I just think of it as a little extra exercise.
The Big Apples are heavy tires, and there are dozens of light, durable road tires you could use instead. If your roads are like ours, I wouldn't go below 1.4 or 1.5--a skinny tire at high pressure will beat you up. Major component swaps just aren't worth the time or money. If you have to replace the crankset anyway, you could save a few ounces there, but do you really need to do that? What do you mean by "turning to mush"? Could new bottom bracket bearings be all you need? If you have a bike that's worth $250 and you put $400 into it, you still have a $250 bike.