Phil,
I wish I could be of greater assistance, I know that my mother's family were in contact with the Spains in the 1950-1960 period. They wer in Australia then, which ties in with your inforamtion that a branch came here.
My mother who is 81 remebers them visiting and thnks that one was NElly Spin, she rememebrs the naem as it was "Nelly" was the same name as her aunt who had been Ellen MAry Abbott before marrying and moving to the USA,
Relatives in USA have a birthday book with Spain birthdays in it. I will contact them and see what they have. This book belonged to Ellen Mary Patterson nee Abbott.
So far I have John Spain b c1851 near Dover marrying 1879 Ellen Mary Abbott b Hampstead 1853.
Children: Ellen S Spain b 1881 and George Spain b 1883,
(source censuses) (could be more)
If it was the daughter Ellen she would have been 70+ when she visited my grandparents.
Ellen Mary had a much younger sister Jessie born c18641 and I found a 1916 marriage between a Jessie C Abbot tand a William A Spain.
Would dearly love to know if there is a double connection there.
Will have a look later at Spin families in the indexes I can access her in Australia and get back to you if I find anything.
regards
Robyn