If I think of "being spiritual" as "being concerned with things of the spirit, eternal things", then I'd say
Rebekah wasn't very spiritual. If being barren bothered her so much, why didn't she pray for herself during those 20 years? I think the fact that Isaac prayed for his wife, and God heard Isaac's prayer and blessed Rebekah with twins is more an indication of Isaac's spirituality. Though to her credit, once she realized she was carrying a set of very active twins, she did "inquire of the Lord." Could it be that having God answer Isaac's prayer by giving her her heart's desire awakened a measure of spirituality within her? or perhaps she was very spiritual, but had been praying to the gods of her people instead of the One and Only God of Israel.
As for Jacob and Esau, I'd say Esau was the more spiritually sensitive of the two. The birthright did have value for him--he wept and begged for it later, but he allowed his carnality, his flesh to get in the way of his spirituality---a situation I'm all too familiar with. Jacob, on the other hand, seemed from first to last to be concerned with "what's best for me?" He doesn't appear to want the birthright because of God's blessings but for the power and the wealth that will come with it. He is indeed grasping and greedy, deceptive and duplicitous. At first. Given the fact that Rebekah's their mother, counteracting any influence Isaac would have had, both boys may have been confused about spiritual things. But Jacob even more so because being Rebekah's favorite, he would have spent more time with her.