Costume jewelry can be just as elegant as fine jewelry and if designed properly, can look like expensive pieces. It's not about being able to afford these pieces, it's about getting the most value for you purchase. You may not want to spend tons of money on something you'll only wear once, especially if you can find something that is just as elegant for a lot less money.
I find it valuable to select fine jewelry when it's a piece that you will wear often and creates new looks for your outfits. I am also the shopper that regardless of the monetary investment I need to put in an item, if I absolutely love it, I will purchase it! I would not say I am materialistic but sometimes purchasing an item will truly make you happier. It's important to reward yourself for your hard work and your accomplishments. It also important to understand the difference between giving symbols to tangible items and being attached to things.