Upgrades from external sources is a risk-laden activity.
Continuous Integration is a form of automation, and automation is dependent on a risk-averse environment.

I would not trust my product development process to be dependent on an automated CPAN upgrade/install/deploy process until my testing and monitoring infrastructure had proved themselves over time. Update: I also suffer no delusions that it would ever truly reach this state.

I think your local PPM cache is a brilliant work-around, and permits you to continue to develop and refine the automation of your CPAN upgrade and testing process as you see fit. If you ever get to the point where you trust that back end automation, you can choose when to integrate that into your PPM cache.

Until then, you're stuck with a mostly-manual process, substituting the time-honored "sweat and blood" for automation, all in the name of reliability. Theoretically, this should keep you motivated to work on those back end upgrade, testing, and monitoring tools. :-)

Or you could settle for releasing crap.

I do hope you saw that last line as sarcasm. :-)