re: Did learning about the War of Roses spoil ASOIAF? ***theoretical spoilers?***

As others have said, the War of the Roses are only one of the inspirations. There are several others - The Red Wedding was inspired by the Black Dinner which was between Scottish factions and was a decade and a half before he War of the Roses. Likewise the Scottish Douglases had "Black Douglases" and "Red Douglases" which is kind of reminiscent of the Targaryans and Blackfyres.

And a whole lot of Got is just GRRM's creation from his own imagination.