Do not book thinking of upgrades. If they come it will be a nice bonus.Never came to me, but I am still happy!
I always try to book ES if I am positively sure, I am going.
I have PG booked for my Euro cruise, because it is far away and I still can cancel with no penalty up to June. But the category I have booked is already sold out anyway, no benefits of the ES expected. There are different benefits with different rate types,
Carnival Conquest February 2014
Carnival Sunshine September 2013
Carnival Valor February 2013
Carnival Valor February 2012
Carnival Liberty January 2010