Sandy, just to be clear, I assume you mean "open" each folder and "build" thumbnails; you are not downloading from a flash card, that's already done?
As far as I know, you have to open one folder at a time, let the thumbs build before going to another folder to do the same. In similar circumstances, I try to arrange to have no more that 150 to 200 images in a folder.
Nice idea though, kind of background thumb building, maybe Mike will comment.

No, it's not misuse, just using a simple work flow, raw to a quality print in as few steps as possible 
Terry.

We need some clarification from Sandy 
Terry

I'm afraid that you do have to wait for each folder to build thumbs in turn. But the good news is it is only done once. Once built, the thumbs appear instantly the next time the folder is opened 

Qimage is now very quick at building thumbs, you can speed it up by reducing the quality and size settings in preferences. I use medium and medium.

Not really sure what you mean here, where would the thumbnail images come from? Qimage builds it's own thumbs and they are linked to the images within the program such that if you move, copy or delete and image, the thumbs are dealt with appropriately. So, the answer is no. 
Terry.