If using DC Miles which are 66%+ Extra for F Class it's not IMHO worth it, especially if Flying on an Airline with Solo Business Class Seats or Long Haul equipment Regionally i.e Upper Deck on a TG 747 or an OZ A330.
If using say UA MilagePlus flying Long Haul which are often as low as 16% Difference between Business and First and you can snag a Highly Rated Airline such as SQ. AN or OZ then its worth the Difference.