Using User Defined Type Instead Of Varchars

A common request for enhancement to applications is to "make this
field bigger". I know I've been caught with increasing a field size,
and then spending hours debugging because another stored proc has a
variable or temp table that uses the field defined as the original
varchar size. SQL Server just truncates to fit the data into the
smaller varchar, and so there are no errors raised.

An option suggested by a colleague is to no longer use varchars, but
use User Defined Types instead. To make this work effectively,
though, they suggest we would need to make it a rule that we do not
use varchars anywhere except to define user defined types.

Though there will be one point of changes I can't help thinking this
isn't a very good idea ! Any thoughts ?

Thanks.