Relative Income within Households

Within couples, if the wife's potential income (based on her demographics) is likely to exceed the husband's, the wife is less likely to be in the labor force and earns less than her potential if she does work. Couples where the wife earns more than the husband are less satisfied with their marriage and are more likely to divorce. Finally, based on time use surveys, the gender gap in non-market work is larger if the wife earns more than the husband.

Source.  

Is income that important in the long run?

1. There is a long run causal effect of income on the degree of democracy. See the paper. See another paper here. The exception is the Muslim world. 
2. There is a long run causal effect of income on corruption. See the paper.
3. Higher income reduces religiosity. 
4. The causality between institutions and development runs in both directions. See the paper. 

Thanks to Andrew Nelson for the pointer.