The gform_field_value_ filter is pretty frustrating, because all that gets passed to it is the value of the field. It would be much more helpful if the filter also passed the field name, the field id and the form object. That would make it much easier to manipulate the field using data encoded in the form, rather than having to hard-code it into a plugin.
(As a work around, I'm aware you can use $wp_current_filter to get the field name, but on its own, that doesn't really help.)
