That really depends on where you are. For me, exit row/prefered seating is a worthwhile upgrade at ~$100/per 12 hr leg, but there are only a few of those seats

That really depends on where you are. For me, exit row/prefered seating is a worthwhile upgrade at ~$100/per 12 hr leg, but there are only a few of those seats on each flight, and they're often unavailable. Premium is double the cost of economy, and business is double the cost of premium. Neither myself nor my employers have that kind of travel budget.