The hubs are most likely Joy Tech cheapies. Any bearing should recieve regular maintaince. The only way yours are goin to slow you down is if they have come out of adjustment.
I over haul mine every 2500 t0 3000 miles. My fronts have radial bearings and the seals can be removed and the bearing cleaned and repacked.
You will find that the cones will have pits in them. It is a problem with cheap hubs. Wheels Manufacturing makes a better quality cone for these hubs.