We are currently in the process of expanding the force to 48 Combat Brigades. We have 37 now. The other problem is utility. During Vietnam we had faced an evolving strategic threat that in some ways better equipped then us. Now days any future threat cannot even hope to fight what we field now and win. A big heavy armor force ready to re fight the 1991 Gulf War would be a huge mistake. We simply face no one able to field such a threat. What we need a more flexible professional force. One that could kick Iran's butt, run Counter Insurgency against Iraqi terrorists and still field a force to contain North Korea all at the same time. We need the right force not just the biggest force. Building the right force takes time. It cannot be done just by snapping the fingers.
Using masses of Conventional Troops in Counter Insurgency missions give you the disasters like Napoleon in Spain or the Russians in Afghanistan more often then not. Some times the important lesson to learn from History is what NOT to do.
Your information is a little out of date. The plan has been reduced to 43 brigades, and those brigades, excepting Stryker and ACR, will only have two maneuver battalions. An option to expand these brigades to three maneuver battalions has been shelved for lack of funding and end strength authorizations.
We could certainly get to a 12 division equivilents with the original 48 brigade plan, but OSD did not allow that to happen. Subsequent to that decision, the Army budget has been cut yet again. No way to get there from here.