If you can hear surface noise or any other effects of stylus wear, you've probably already done permanent damage to your vinyl.
Assuming clean vinyl and proper setup, the main factor in maximizing stylus life is the size and shape of the stylus. The larger the contact area, the less friction at any given point and the longer the stylus will last. Conical (spherical) styli have the smallest contact patch (theoretically a geometric point) and therefore the shortest expected life. Elliptical styli are better. Line contact stlyi are better yet and micro-ridge styli should last longest of all, since they have the largest contact surface. The makers of a few, high end micro-ridge styli even go the extent of aligning the ridges with the molecular structure of the diamond, which makes them significantly more resistant to friction.
Stereo shops used to have specialized binocular microscopes for stylus inspection. Even with that it takes a trained eye to know what to look for, and fewer shops have those tools and skills any more. We have one locally but many cities do not. You could consider mailing it to the manufacturer or one of the respected retippers, like Soundsmith for example. They'd give you an honest assessment.
An audio signal analyzer or software could probably be used for this also, assuming you had data from a new sample of the same cartidge to compare. A worn stylus would start to lose HF response, beginning with highest frequencies the cartridge can reproduce. The more wear, the more this would progress. You can't wait until you hear this however. Most cartridges extend well above 20KHz, so by the time you noticed HF rolloff much damage could have been done.
