Short answer: Yes it is.
Many times you can get just as much money for your "used" costume jewelry as your "used" fine jewelry. Typically, a jeweler will only give you the scrap price for your fine jewelry. Scrap price is a percentage of whatever gold or silver is selling per ounce that day. For a reasonably heavy mans 14K gold ring today, you might get $100.00 from a jeweler.
For costume jewelry, it is more complex. The value of costume jewelry is determined by how old it is, whether it is made by a collectible designer (and is signed), and it's condition. Older costume jewelry has more value especially if it is art deco or victorian. If it is signed, it has more value than an unsigned piece. And used jewelry that doesn't show much wear to the metal finish, or missing rhinestones, is more valuable than a piece that is discolored.
When someone brings a box of jewelry into my store, I weed out the fine gold and silver pieces. Then I separate them all into category by decade. I check each decade group for a makers mark, or whether it is signed. Then I separate out the damaged pieces. Then I get my jewelry books out, and start looking up the makers to determine the value of each designer piece.
Older victorian costume jewelry pieces typically sell for more than the 14K gold mens ring at scrap price. Many signed 40s or 50s rhinestone brooches sell for more than fine gold jewelry at scrap price. There are many collectible 80s pieces of jewelry that sell for over $100.00. Therefore, it is important that you know something about your old used costume jewelry before you put it in your garage sale, or take it to the church rummage sale.
How do find out about your jewelry? First, ask around and find a reputable honest jeweler who will tell you which pieces are real gold and silver. They can also tell you which pieces are older, and might have significant antique value. Next, go to Barnes & Noble and find a collectible vintage jewelry book. There are many out there, and my personal favorite is "How to Be A Jewelry Detective" which has all the pertinent information to identify rare pieces of jewelry when you are out there bargain hunting.