If goal is Grand Prize #3. Best bet would be always spending Tickets on Double Gooo days.
And as you said, on the lower Chests, specially the one that offers chance to get more Tickets.
Never go for the higher % Chests, the higher % is for Daily Buildings, which isn't your goal.
Always get the Chest that offers the most Goo for the least amount of Tickets.
Of course to optimize the Set, you need a 4th building, which is one of the Dailies, here also. You should try for the lower % Chest with highest Goo. And hope you get that Daily Building.
If this method is used throughout the whole Event. Chances of getting Gp 3 are high.
But yes, it's possible to not get it also. Luck plays a roll with these Events.
Good luck!