To us futurists, the idea of space and time travel is fascinating. Or should it be
To we futurists, the idea of space and time travel is fascinating.
"We" is correct the form. In your example, "we" is a determinative used to mark the noun as definite. It denotes a set containing the speaker. But do not confuse determinative "we" with pronoun "we" used as an appositive:
To we futurists, the idea .... [determinative] To we, the futurists, the idea ... [pronoun, appositive]