I came across this in my reading on this site and I am sure you have probably heard it before but I wondered if it might help with fresh ideas.
In what ways could you "package" your thoughts, idea, and even yourself, to appeal more to the "buyer" (your partner)? Are you planting any seeds towards peaking their interests? Are you losing any "sales" because you're trying to sell them in a way that would make YOU want to buy instead of a way that appeals more to THEIR interests?
What ARE some of your partner's real interests? What things do they seem to come alive over, that really excite them? What things, and subjects, can they start talking about, and it's hard to get them to shut up? What kind of projects can they really focus on, and get lost in doing?
I thought it may help in selling the MC idea - although I know that would be a hard one!
I agree with what Michelle says, doing things without her 'approval' is a 180 and it has got her attention in the past - remember when you went out yourself for a meal a few months back. The thing I wonder with your wife though is whether sometimes she feels excluded - being that there are so many men in the house? What were the things you did together when you first started dating? How about sparking her interest more by going taking one or more of the kids out to something she would be interested in - the cinema or something - and then next time inviting her. You could state it in a more independent way like
'I was going to take S? to see (a film that is not to boy orientated!). I (you are saying I here not we as in the kids) would really love it if you came too?'