1. You're right, you weigh the damage and risk against the value, many types of item damage can't be helped, but dirt from under glaze? I'm sure many people do that. Even so I shouldn't have advised that to a general audience, even with experience it can go wrong - It was irresponsible and I apologize.
2. as per Kovels the terms Spatterware and Spongeware are pretty interchangeable, see below:
"Spatterware and spongeware are terms that have changed in meaning in recent years, causing much confusion for collectors. Some say that spatterware is the term used by Americans, sponged ware or spongeware by the English. The earliest pieces were made in the late eighteenth century, but most of the spatterware found today was made from about 1800 to 1850. Early spatterware was made in the Staffordshire district of England for sale in America. Collectors also use the word spatterware to refer to kitchen crockery with added spatter made in America during the late nineteenth and early twentieth centuries. Spongeware is very similar to spatterware in appearance. Designs were applied to ceramics by daubing the color on with a sponge or cloth. Many collectors do not differentiate between spongeware and spatterware and use the names interchangeably. Modern pottery is being made to resemble old spatterware and spongeware, but careful examination will show it is new. Many spatterware pieces are painted by hand and often picture flower, bird, and house motifs. "
