I didn't realize you wanted this as an expression to control the smooth levels. That will slow things down, probably by quite a lot, although I've never tried it this way.
Your best bet is to make a direct connection from your control attribute to your smooth nodes. Simply add an extra attribute to a control object, and then use the connection editor to connect this new attribute (a int, not float) to the divisions of the polySmoothFace node.
Because you have 30, this might take a while, but the end result will work a lot better than an expression.

You could probably write a simple MEL script to set it all up for you, similar to what I wrote below but change the loop to connect the attributes, instead of set them.


Richard