After looking around the web for an SQLalchemy model migration assistant, we found no satisfactory equivalent to the migration tool that people love for Ruby.
In particular sqlalchemy-migrate seems like it's an overkill (in addition, sqlalchemy-migrate is fiddly to set up with Pylons).
There's also a project call miruku, but that is also a little illusive, somehow.
PLATFORMedia has published a simple 150 line script that parses the Pylons INI file (augmented with a line that points to the model.metadata variable definition), and allows just two actions :
diff the current database vs. the what the models want
commit the changes required to bring the two into sync.
The script is dependent on sqlalchemy-migrate, but it would probably sit better as a Paster-Pylons plug-in.
It is located at http://github.com/mdda/sqlalchemy-migrate-pylons.