Performance implications of numeric?

We have a lot of tables which store numeric data. These tables all use the
numeric type, where the values are 95% integer values. We used numeric
because it eliminated the need for casting during division to yield a
floating point value.

I'm curious as to whether this would have performance and/or disk size
implications. Would converting these columns to integer (or double
precision on the handful that require the precision) and forcing developers
to use explicit casting be worth the time?

Thanks for any clarification.

--
Wells Oliver
wellsoliver(at)gmail(dot)com