For that kind of upgrade, yes. It looks to me like you're just being quoted a fare rules upgrade, which consists of the difference between the WT+ and CW fares plus the change fee applicable to your WT+ ticket. So if there is a sale and if in the sale you could buy the CW ticket for the same flight(s) at a lower amount, then it would follow that the fare difference for an upgrade would reduce by the same amount too.