I travel through Blonduos every time I'm in the area, something which requires little effort as the city is located directly on Route 1 which goes all round Iceland.
Generally, when I think about Blonduos, the first image that comes to mind is that of the church with its massive cross proudly anchored in the ground as well as its modern and original style. It's like a type of concrete coil! The town centre seems to be divided in two, standing on either side of the river. It has small, quiet streets and a very shabby hotel which still seems to work.
I haven't visited all the museums in the city but I know there are museums about ice, textiles, and salmon. The latter is what gives the city its reputation. As for the restaurants, make sure you stop in at Potturinn, the little brother of the one in Reykjavik.