The final (varargs) add-vectors function in the OP is clearly (at least to me) more terse and readable than the original (2 arg) one. I've only written a coupl

The final (varargs) add-vectors function in the OP is clearly (at least to me) more terse and readable than the original (2 arg) one. I've only written a couple thousand lines of Clojure to date, but code like that already just looks right. The varargs version has less possibilities for errors; the 2 arg version allows for several permutations of first/second to be written incorrectly, or the wrong va/vb used.