That's €600 OW, so €1200 RT + original price. Say it's a total of €2k if upgraded both ways VS €3k if bought in advance, there are some notable differences between guaranteed C booked in advance, with ALL the benefits (miles, luggage, what happens in case of IROPS) VS. an upgraded Y ticket. Eveyone perceives the value differently and can decide if it's worth it, of course, but there are differences.