If you want to make money with Shapeways DON'T BE A JEWELER! HAHA!
If you're lucky and you find some niche jewelry items that people buy and you can get lucky numerous times for various designs you could easily make a living at it. Otherwise you're going to make Jack Diddley.
You can however make money with jewelry designs if you are extremely extremely talented. On very rare occasions I run into jewelry designers on Etsy that I would consider to have this level of talent. They always appear in the trending sections of Etsy and you can tell by looking at the sales in their shops that they are doing very well.
One area though that sells very well and you don't need to find niche items is miniatures. There are so many hobbyists in the world that have this subject as a hobby that just about anything you make in miniature form will sell. Some of the top-selling shops on Shapeways are selling miniatures. Another area that is pretty good is anything having to do with games. Things like dice, boardgame components, Lego items, poseable dolls and so on. I think probably (no way to tell for sure because it is a secret ) the number one selling item on Shapeways is the
Thorn Dice Set sold by Ceramicwombat, which is a game related item. Then there are the collectors. A perfect example of this category would be accessories for Transformers figurines.
You can make money with Shapeways but you need to be superduper smart when it comes to deciding what you're going to spend your time on. I know that there are a few shops whose owners are making a living from Shapeways.
I think you're right though in your assumption concerning traffic within Shapeways shops as compared to the number of stated items being printed every month. I think most of Shapeways customers are people that are using Shapeways 3D printing service for doing rapid prototyping. This is because Shapeways has the lowest price in the world when it comes to 3D printed items so people from all over the world flock to Shapeways to get there prototypes made and those people never visit the Shapeways shops. Over the years I have seen Shapeways make business moves that proves that their main income is not coming from the shops at all, rather it is coming from these rapid prototyping customers. I am getting proven traffic to my shop though, probably the best place in the world right now to sell items online that is compatible with 3D printing would be Etsy. Etsy is HUGE! When I compare the sales that I get from my jewelry items on Etsy and Shapeways the sales are roughly the same. So that right there tells me that Shapeways is getting just as much traffic to my Shapeways shop as Etsy is getting for my Etsy shop. So in this regard Shapeways is very up to par as far as traffic is concerned for my Shapeways Universe Becoming shop.
Oh, and one other point about traffic concerning Shapeways. I have a number of the same jewelry items in five different Shapeways clone companies around the world. I get zero sales from all five of these other shops, so that too would be an indication that Shapeways is doing well when it comes to getting traffic for my Shapeways Universe Becoming shop. If you would like to see actual numbers here is a screen cap of my Google Analytics data for traffic that I've had in my Shapeways Universe Becoming shop year to date.
Don't give up! There's plenty of money out there to be had via Shapeways, you just need to be extra clever in order to get it.