Yes, the Wizarding World seems to have somewhat antiquated ideals and traditions. But bear in mind that half of the founders were female and that there were women who were heads of the government, the school, and St Mungo's in the 1700s, which hardly fits the obedient meek, wife template. Narcissa doesn't appear to work, but then again, neither does Lucius, and women within the Wizarding World have been working for longer than in the Muggle World.

To me, it's one thing to say that people are expected to remain faithful to their spouse (something I honestly feel has a magical connotation), that there is not likely to be divorce, and to not manipulate the emotions of someone close to them, and another entirely to assume that Narcissa was a shrinkng wallflower. Narcissa is a Black FIRST, then a Malfoy, and Walburga could hardly be called weak or passive. Aramina Meliflua was apparently in government, and I got the impression that was at least fifty years before his conversation with Harry about it.

I absolutely agree that the Ministry would be suspicious of Lucius. I can absolutely see the Ministry raiding Malfoy Manor and the Malfoys privately being incredibly put out about this, although I think publically, they would appear to cooperate in every way (you know, one of them ensuring they're fully accomodated while another is off hiding things that could incriminate them or that they wished to keep for whatever reason). However, I sincerely doubt that Narcissa wouldn't want to regain their position, provided she could do it without endangering the life of her son.

Remember, these are die-hard born and bred Slytherins. They look out for themselves. Given the choice between extinction and position, they'll choose life, but with extinction not an option, they'll absolutely vie for position. Their wealth, their standing, their name, was very, very important to all three of them.