Having lived and worked in Spain, I have to say that although they partially work in some cases, non of them really cover the meaning implied when calling someone simpatico, imo.
OK. I can't say I'm particularly familiar with the word. When I saw those definitions it made me think of the advert for affinity.com where the guy and girl are in a shoe shop and accidentally tie their shows together, and they defined affinity as something similar. Though, I'm more familiar with affinity meaning a particular fondness for someone/thing.