The name "Spesco" doesn't mean much - that would be the importer or distributor. The key is "COMPANHIA BRASILEIRA DE CARTUCHOS" which translates loosly as "Brazilian Cartridge Company" and is the manufacturer. I have heard that name before, but I can't remember where, and I can't find it in my reference books. It is commonly referred to as CBC. The company does have a web site: http://www.cbc.com.br/explorer.htm
There could be exceptions, but I believe the CBC guns are the cheapest of the cheap. They are the K-Mart Bargain Basement of guns. And a single-barrel is generally the cheapest type of shotgun. I don't mean to imply that it is a "bad" gun - that certainly isn't true. If it is in good condition it should be a good shooter. But it is not a collector's item.
The gun has a lot of value to you as a memento of your grandfather. Keep it and treasure it for that reason. If it is in good shape, use it in his honor. There is no need to insure it or sell it, because it isn't worth that much anyway.