Are there benefits to having greater genetic differences between parents?

Beyond the problems of inbreeding (e.g. marrying a cousin, sister) is it beneficial to offspring for parents to be highly genetically dissimilar? For instance it might lead to offspring with immunities to more diseases.

I also heard somewhere that if a couple has multiple children that have strong resemblance to each other this is a sign that the parents are very genetically similar. Conversely, I heard that if siblings of the same parents do not look alike this is a sign that there was a wide genetic variation in the parents (i.e. lots of traits to choose from). Is this true?