Except for the exposure adjustment brush, the LR4 adjustment brushes seem to make only very small changes. For example the temperature and tint adjustment brushes often don't make much of a difference. I wish they could make bigger changes.
At what level is the flow slider set when using the adjustment brushes? Also, clicking the disclosure arrow immediately below the 'EDIT' text, reveals a 'volume' control which can alter the power of the effect. When I use both controls set to 100, the effect on colour temp. is significant (ie. great big colour cast!)