Fenders will do precisely nothing to protect your bottom bracket. Doesn't mean they're a bad idea, but in general buying fenders with the expectation of reducing maintenance is misguided, except probably the headset. When you say you cleaned the bottom bracket, what do you mean? Did you pull out the bearings and install new ones? Because that's not generally worthwhile with a GXP or other sealed outboard bearing BB.
Originally Posted by
tarwheel
Do you need fenders? No. Would they make your commute more enjoyable? Probably. Would they keep you bike in better condition? Certainly. To me, the main advantage to fenders is they help keep your bike clean and prevent dirt, grime, grit, water, etc. from fouling up your drivetrain. Notice that I said "help." Fenders are not a magic bullet that will prevent you from ever having to maintain your bike, replace a chain, etc. However, they will certainly help keep your drivetrain cleaner, better functioning and long lasting.
Full-coverage fenders certainly help keep you more comfortable, but I'm always surprised anyone seriously argues that they keep the drivetrain cleaner. In my experience, pretty much everything at hub level or below still gets pretty gross. Maybe it's not as bad, but it's really a difference of degree.