It's true that NH has traditionally been in the top-tier of states when it comes to median household income. In the 2016 ACS, it appears to have reached the top:
But its lead is not an overwhelming one. Connecticut's 2016 median hh income was just ~$350 less. According to the the previous ACS in 2015, NH was number 8. And 6 of the top 7 were traditionally blue states.