I agree with your husband mostly Michelle! I don't use my metal shim all the time- just for those hard to cut dies?? For a lot of dies the metal shim isn't necessary.
The thing I wonder is this .. . the dies that we use I wouldn't call "sharp", kwim? They have a metal edge but we're not really afraid of getting cut right? (now I that some of them have sharp edges, etc., but for the most part they aren't knife sharp). The reason they cut, is a lot due to pressure. So do you think we still need to worry about them "dulling" (is that a word??)