Generally prices only ever go up.. not down!
And for most RTW fares, they generally a tweak in their fares every May and Nov. Well that was the case way back around 2000-2005. Now, with currency depreciation, airlines can't wait to hike up the fares and 'forget' to lower them when the said currency appreciates!
I can't afford a RTW these days in coach, much less in premium classes. How sad.