I agree too, there are many examples of gambling or spiritual objects that appear in a usable size and then also in small versions, many times used as jewelry.
And one thing I noticed is that the small versions of the dodecahedrons are also found in pendents or other jewelry.
Modern? Hell, how about a Roman one that’s obviously multi-purpose…
And also especially for someone who doesn’t know about hex-head nuts and bolts. It may be that there’s some other tool or item that these things are meant to be used with, but those were typically made of less durable materials.
My pet theory is that it was a die with the added use in augury. I think the item could be repourposed like a modern 64 square board that can be used either with checker or chess board pieces. Yes, a bit more complex, but then (Obelix from Asterix an Obelix) “Romans were crazy!”.
Now I think that the knobs were used to help keep the named pieces that could include the zodiac, names, or fortunes in place. I think that the pieces were kept in place using string and the holes kept the pieces in place too with protruding bits under the pieces.
Pieces that were not as lasting as the metal “board”.
If it were a die, wouldn’t the faces be clearly distinguished from each other? Surely they didn’t grab a micrometer after each throw to determine which of the similarly-sized holes was facing up.
Holy!!!
Yes, i immediately recognize that as a multi purpose tool.
Sometimes it’s both a floor wax and a dessert topping. I think the design may have been used for multiple purposes but I’m not leaning towards it being a tool or utility item. Ritual, gaming, even a fad like a pet rock or a status symbol. And maybe the purpose changed over time. Maybe if you had one sitting on a shelf and someone saw it they ask “Are you a dodecahedron?” and club members would answer “You bet your sweet ass I am”.
If it were a die, I don’t think there would be examples that are the size of a grapefruit.
If it were a die, there wouldn’t be knobs at the corners making it near-impossible to actually roll.
Again, Romans were crazy. 
But seriously, the other articles I cited about Roman dice, point at the Romans not caring much about how distinguished the faces in their gambling or augur implements were.
Again, there are many examples of dice or other items for games and augurs that come in miniature size.
And conversely:
Why do boneheads like to show up at my weekly game night with these ridiculous 45mm solid metal table-denting miniature-smashing d20s? You can get even bigger plastic or resin ones.
At least you can roll that. Putting knobs on the corners of a die is like putting square wheels on a chariot.
The Romans had dice; they look like dice.
The wood pieces [most likely material] would go in the faces right between the knobs, with string or other holders also using those knobs. Of course, it is just a pet theory, but I would think the Romans had a clever way to keep those pieces in place temporarily and allowing other soldiers or people to “bring their own” pieces to be be used.
What would be the point of making all the holes in the faces in different sizes, and decorating the faces with inscribed lines, if the intention was to cover that up with wooden plates?
A toy or game with shapes that go in holes in the sides of a dodecahedron seems overly complic…
I take that back.
IIUC the size changes are due to the making of the dodecahedrons. Some plates would fit better, others do not. As the articles cited mention, Romans did not care much about fair dice or for other augur or gambling items, they cared more about convenience by carving the six peeps on the wider side of a blank die.
And another thought just came to me: Romans that did not care about odds would had liked to toss a thing like that and not roll much, they needed their augurs-fortunes-winnings sooner rather than later.
The problem with Roman Dodecahedrons being shape sorters is the same as this one:
I feel like if there is one thing we can say with reasonable certainty, it is that the differing hole sizes are a deliberate choice, not an accident of manufacture.
IIRC there was a report of the different sizes as being the result of saving material first and them carving the other ones to size. But if it was on purpose, one possibility is that the holders that I’m picturing could had been the pieces having hooks or tied to each opposite side, with the large holes used to make it easier to access the knots after the game or augur was over.