you must be seriously bored of window cleaning to even consider this sort of work IMO
Yes, I guess we're both bored of it. Same places, same faces, same things.
That also could very much turn out to be the same faces, same pylon, same paint, but harder work and for the same pay?
I agree with one of the posts above (think it was dazmond) that if a newbie came on here saying he wanted to quit his job and start window cleaning, we all would be telling him to do this on weekends and see how he goes. Test the water. It's not for everybody.
I think the wisest course is to let your wife test the water while you stay with the windows. If after 6 months it turns out like you hope, then it's a no brainer.
I do think the pull of being your own boss is a huge one though.