The expansion should allow for the larger cruiseships to go through the canal. I don't think that a big change in cruising will occur because there might not be enough demand for the larger ships on the Pacific Coast.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!
Probably the biggest change will be the increased cruise fares for these trips.
Building those new locks cost a great deal of money. Somebody has to pay for them.
When my ship went through in April (one way), we paid just over $400,000.
The Canal Authority is predicting a 20% price increase next year.