A more interesting question, perhaps, is whether it is good public policy to drive out retirees, particularly wealthier retirees. Granted, the elderly don't produce much and consume a lot in services. On the other hand, they are (usually) living off investment income and transfer payments, which are spent in their home state. Their heavy consumption of health care is mostly paid for by Medicare and employs doctors and a host of other health care providers. They don't send kids to the public schools. I haven't done a detailed analysis, but my guess is that they're a net plus for the economy.
Little in Nebraska's tax policy makes much sense, but this seems particularly short sighted.