Well Thingiverse is at the moment in my opinion a great way to share your 3D files, I would personaly hate if they ever would charge you for STL files,
This would also create another black market for Torrent STLs,

They could give the User a fee if they would get up some Adverts, Like a Ad.fy (Thought it was named like that) that you have a page with adverts and gotta wait 3 sec before you can download it,
This way they would get a few cents every download, But i would certainly not like if they would ask like 1-5 dollars for a design that you have to print wich is another 5-8 euro to print sometime depending on what your printing.

If you realy want to get money create a shop, don't ask Thingiverse to change the idealism they have at the moment just due you would want to earn 2 easy cents.
I would be for the Advert thing, but totaly against a shop like Appmarket and such.

I also have a few designs up in the air, I don't mind it i just wanna share them so others can enjoy them as i did/do.
Even tho with a Advert system i wouldnt mind earning a few cents of course, But i wouldnt ask money for a STL file.