I'm wondering if you good people have any suggestions that might
help me keep them nice and sharp for longer?
I suspect that the rubber base may require you to hit the stamp
substantially harder. That would reflect more impact back to the
stamp, but would also cause more distortion of the shape of the item
you're stamping, though the rubber will prevent the back surface of
what you're stamping from picking up a mark from a firmer surface. If
you could use something more like a polished brass surface, either
flat or shaped to support the shape of what you're stamping, you may
need less force to get a good impression.
But I'm guessing that isn't the problem with dulling stamps. More
likely, you're just using less expensive, lower quality stamps. There
are some on the market, typically they are made of round steel stock,
sometimes nickle or chrome or some other electroplate finish. They're
steel, but not as carefully heat treated as good stamps. The good
ones are characterized by being usually square or rectangle tool
steel, usually black in color from heat treatment. The impressions
are cut clearer and deeper than the cheap stamps. And these things
are not the cheap 8 dollar (random number pulled from my old head.
Not sure what those cost now) ones. I have some of that better sort
that I've had for 30 years, and they work almost like new. Of course,
there are exceptions. Some metals, especially the harder ones like
white golds or rose golds, titanium, steels, etc, simply are hard
enough that stamps will wear. But just a year? Sounds like a junky
stamp to me...