Antonyms of spicy:
unsexy, tasteless, cold, flat, insipid, stale, dull, flavorless, prosy, stupid, vapid, clean, decent, g-rated, nonobscene, innocuous, inoffensive, priggish, prim, prudish, puritanical, staid, straitlaced, victorian, correct, decorous, genteel, nice, polite, proper, respectable, seemly.
Examples of usage:
  1. Seems pretty ancient and spicy, don't it?"
    "Queen Sheba's Ring", H. Rider Haggard.
  2. The scent had an indescribably tingling, spicy odor, and left a cool and grateful sensation in one's parched and dry throat.
    "A Woman Named Smith", Marie Conway Oemler.
  3. The cool north wind wafted the spicy odor of the cinnamon roses to my nostrils; but- alas for the prosaic fact!
    "A Rambler's lease", Bradford Torrey.