I expect there would be two kinds of jewelry:  Sentimental jewelry and fresh jewelry.

**Sentimental jewelry** would be purchased once, and kept/worn for a very long time.  The value to the wearer is in the memory of the occasion on which it was received or purchased.  For example:  class rings, engagement rings, wedding rings, military medals, Super Bowl rings, *et cetera*.  These pieces of jewelry would be made out of materials that can handle wear-and-tear.  Using today's pricing, they might be more expensive than today's jewelry (e.g., 18 karat gold instead of 14 karat gold, or 3 carat ideal-cut diamonds instead of ½ carat diamonds whose cut has been compromised to avoid "waste").  They might even have carefully designed "flaws" to make them unique.  But they would still be made out relatively durable materials (such as 18 karat gold instead of pure gold, or diamond instead of cubic zirconium).

**Fresh jewelry** would be designed for optimal beauty when new, and replaced promptly (before it has a chance to wear out).  It is possible to make cubic zirconium gems that have purer colors, more fire, and more lustre than any ideal-cut diamond.  The problem is that cubic zirconium is softer, so after a fair amount of wear-and-tear, these hypothetical gems would not be as pretty as the ideal-cut diamonds.  Similarly, one could have 24-karat gold plated items instead of brass, bronze, or gold alloys.  They might be flawless, or they might have designed-in "flaws" similar to the sentimental jewelry.  Thus, "costume" jewelry would be much higher quality than any jewelry made today, but it would not be expected to last long at all.