we have found that DTSConfig files work great for storing the parameters for the database, as you don't very often move your application from one database server to another except during upgrades and lease refreshes, so that file remains fairly static by environment.

we use SSIS Configurations table in SQL to store all other "variable" data such as flat file paths and that gives us the ability to manage the values programmatically or via SSIS to move changes up into test and prod from dev. plus it's very easy to write an update query to change your path with a few well placed charindex and substring or replace statements

we also call all our jobs via a production scheduler using dtexec passing the config file into the command line.

This also allows you to only need control over dev and test, and when you we need something promoted to production you can just ask the DBA team to copy the dtsx file from test to prod, and leave the dtsconfig file alone.