I'll answer that. Never. It is never wise to go all in on a crap shoot. Trading to get Ohtani woud only marginally boost our odds to win the World Series. It would also cost so much that it would reduce our odds of fielding a playoff caliber team for the next few years. It is a fools errand.
That isn't to say all trades are bad. Nor is trading for a "needle mover" by definition always wrong. What is always wrong is doing so because of the "this is our year" mentality. Nobody knows which year is "the" year until its over. Believing one year is the year is magical thinking. You don't change the organizational philosophy that is considered one of, it not the, best, most competently run organizations in the the league based on a belief in fairy dust and unicorns.