One of the problems with a worn stylus is the fact that it is now damaging your records. This can be something that is initially not that noticeable, until such time as you replace the cartridge or stylus and hear the groove damage!
Probably a good rule of thumb is to consider replacing the stylus and/or cartridge after a certain amount of time ( depending on the stylus shape) regardless of what condition it might appear to be.
I would think if at all possible, a re-build by the original manufacturer ( if in budget) would be preferable, simply because they have the exact specs and access to the original parts.