I must disagree with the discussion so far.
While at first it seems that you can exploit Quest for the New World to get some quick exploration, the reality is that by itself, Quest for the New World is not enough to have a great colonial empire.
As Castile, I found myself needing three national ideas to make a truly powerful colonial empire in Central America. First, I needed Quest for the New World just to find the New World. Second, I needed Deus Vult in order to DOW the meso -Americans without need for a CB. Finally, when I owned everything from Nevada to Panama, I had to take Viceroys in order to make the provinces in any way profitable. Furthermore, as leaders began to die off, I needed to continue purchasing conquistadors in order to enforce policy in Latin America through killing natives and planning my next war of conquest against the Incas, so it was not feasible to swap out National Ideas. Stability costs were already fairly high, and a -3 hit to stability would have meant perpetual revolts in Latin America for the next decade.
Think about that for a second. I needed three national ideas to set up and make a colonial empire truly profitable. That means I had to miss out on Conscription (extra manpower), Military Drill (extra morale), and Scientific Revolution (cheaper research), which I would have taken as Austria or Poland. Needless to say, I kept very strong diplomatic and military ties with Portugal and Aragon in order to convince France to leave me alone.
And I needed those three national ideas just to get to the same place Spain did historically (except that I never managed to become Spain for some reason). I don't see this as being too unbalanced.