My suggestion is simple. Make it possible to toggle membercards when clicking on user profile. This setting should be available as global and local.
Forum administrator would be able to turn membercards off completly and users couldn't turn them on for themselves. However, if membercars are turned on globally, every user should be able to disable them in their preferences.
I'm probably not the only one who would like to go on user's profile directly without seeing membercard or openning new tab, so I think that this suggestion is actually useful.