If your Shimano bottom bracket is a sqaure taper style, I wouldn't worry about reusing it. Shimano stopped using square taper cranks on their better groups back when they upgraded to 9 speed, so a squre taper Shimano bottom bracket is 2 generations old if it is 105 or better quality. If it is lower quality, it may not be worth re using. Campagnolo is not necessarily more expensive, but it does have the virtue that shifters can be rebuilt when they wear out, which makes them more economical long term.