I generally use a few different steps to clean a cartridge, starting from the least aggressive to the most:
- Rubbing alcohol
- Pencil eraser
- gasoline/WD-40/carburetor cleaner/brake cleaner (whichever's handy)
- fine sandpaper
You cant really save a NES whose contacts have bent from years of use though.
Of course you can!. Bend the pins back into place, get a replacement cartridge connector (I'm pretty sure they still manufacture new ones), or you can build a new connector using two really old floppy cables if you're feeling ambitious. Replacing the cartridge connector itself is the easiest method. It's just a C-shaped piece of plastic, and the motherboard connector is basically another cartridge connector. Take the motherboard out, slip the old connector off, slip the new one on, reassemble.
Besides, most of the failures in the NES are because of the lockout chip, the problem isn't always the cartridge connector. If you disable it (simply cut one leg on the IC off the motherboard and short it to ground), your NES will be several times more reliable. "The blinkies" are caused by the lockout chip resetting the console because it can't talk to its counterpart in the cartridge properly.