It's been reported (it's not where I thought it was and I can't find it) that the Holy Fathe intends to keep the number of new cardinal-electors small enough to conform with the 120-elector limit. As we all know, John Paul II didn't pay much attention to it.
However, 120 cardinal-electors is not a bad thing. Rewind back to last April when all the cardinals showed up in Rome. There were all the stories floating around about how due to the global Church, cardinals didn't know each other and there was a flurry of hurried 'get to know you' sessions in addition to the Meetings prior to the conclave.
120 men is right around the right number for everyone to know each other on a good enough basis so that when the big event rolls around, people aren't forced to tack on the 'My name is X' tags. The US Senate is at 100 members. Here in Iowa, the state house has 100 members and the state senate has 50.
It's true that the more cardinals there are, the better represented the Church is as a whole across the world when conclaves come up. But representation can be provided for not necessarily by adding cardinals but by redistributing the red hats. Some thought will need to be put into making sure there are hats in the right places while at the same time making sure that everyone will know everyone else.