It doesn't increase the chance of spinning a rod bearing what it does is weaken the crank because you are removing material. If it is done well it won't weaken the crank enough that you would ever have a problem with it. That being said there are companies that sell light weight Honda cranks. About balancing, Honda does a great job of balancing the factory equipment you really don't need to balance the rotating assembly unless you have changed something there (pistons or rods, but not pulleys or a flywheel as these should be balanced when you get them). You can take a machine shop your entire rotating assembly (PP, clutch, flywheel, crank, rods, pistons, rings, and crank pulley) and have them balance the entire thing. I am planning on this after I get pistons and rods.