The "maim" sound isn't too attractive. mamie feels more like a nn and less like a full name than say, Molly or even Maggie.
It also has an unpleasant racial association; whether it's because of some character I don't know about, or the fact it's very close to "mammy" it has a rather stereotypical and potentially condescending vibe to it.
Also, it just plain sounds like baby talk.
Before you criticize a man, walk a mile in his shoes. That way, when you criticize him, you're a mile away and you have his shoes!
Steve Martin