Green Card or Citizenship and moving to Spain

[jilltim]

Looking for a bit of advice. I think I know some of the answer but since it is a little confusing I wanted to clarify. Right now I have been in the USA for 20 years and have had a green card the entire time. Apart from some time between jobs I have been working. I am a UK citizen and have considered getting US citizenship off and on for the past few years (my wife is a citizen of the US) and thus have dual. My situation is starting become unclear since now we are both starting to plan a move to Spain and start our own business. We do not have children and since we are in our mid 40's we are some distance from qualifying for SS. Earning wise we have not nor do we expect to have yearly earnings in the future that would place us having to pay US tax once working in Spain. My question is mainly does it make sense for me to obtain US Citizenship prior to leaving the US? We do not plan to return once we leave but as I understand it without US citizenship I would be hit with a 30% tax on 85% of SS once I am eligible and could not return to the US without filing for a Visa after a year or two has passed. Of course, it seems very likely that SS retirement funds will not exist by the time we reach retirement and we will have just our 401K and IRA money. Perhaps I keep my Green Card and serender it once we have filed our first 1040 outside the US (thus reducing my need to file tax returns to the US)?