Maybe this workaround from Debra Dalgleish's site:
http://contextures.com/xlDataVal08.html#Larger

"Capt. Cave Man" wrote:

All the help I could find allows me to change the font and size of a
drop down list in the excel toolbar. What I want to do is change the
font and size of a validation list in the worksheet itself.

I was unable to find any reference to it. I have a list that points at
a named range for the hour of the day, but my drop down list is so tiny I
can barely read it.

Does anyone know how I can change it.

For that matter, the information boxes that are part of the validation
dialog pops up in a box I would like to size and even change the color
of.

Can that be done, or is it tied to the Windows OS help system or
something?

--

Dave Peterson