I'm going to throw 2 cents in here.
I know it seems strange that you got invited to a shower for someone you barely know. I can recall my mother telling me that "in her day" any female that got invited to the wedding got invited to the shower, and you NEVER invited anyone to a shower if oyu weren't inviting them to the wedding. My guess is whomever is planning this shower s working under that "rule".
If you don't want to go, I would say RSVP bthat you Can't go because of a prior commitment, but I would send a gift. Not because you got invited, but because the groom is a friend/co-worker of your husband. I'm not saying the gift has to cost $5000, but a small gesture would probably "keep the peace" all around.
That's what I'd do, anyway. I thnk it's important to have a good relationship with your spouse's co-workers.