One hour is never enough to do anything with tumbling.  I ran for 5-6 hours with mine, which was annoying because my dryer can't be set for more than 45 minutes at a time.  Also tumbling is only suitable more robust parts.  I think it can make a good companion to acetone vapor however.  Use the vapor to remove the layer lines, and then tumble to get a matte finish if you want it.  You can walk away from the tumbler, but the bead blaster takes a lot of time and effort to get a consistent finish.

This is as we suspected. I think the acetone bath is best option at this point.

Somewhere on here IanJohnson tried tumbling with a setup in his dryer with no heat.

I tried a Harbor Freight vibratory tumbler with ceramic media, but after an hour or so, there was very little change in the surface.  The acetone vapor bath works well, but you only get one shot.  First time, I had too much acetone in the bottom, and when I heated it up, it expanded and bathed the foot of the print in pure acetone.

I think they're too big for what you're doing with them unless you have only larger prints

Sounds like it. They are way too big. They do sell less aggressive plastic blasting beads, but the walnut shells are softer than even those.

Where are you guys getting your pellets from?  What size are they?  They only problem with this idea is the pellets would definitely break down so they'd have to be replaced regularly.  Still might be worth it though. Probably need 5-10 gallons to start with. Maybe 10-20 pounds?

eBay. $2.50/lb, shipped. Roughly 3mm x 3mm x 3mm.

Could you use the ABS pellets that we are using in the filastruder thread?  They are pretty cheap and you will get so much reuse.  You could get clear, white or black too.  So that way you might even be able to polish it with plastic pellets of the same color of the print.