Hi Kristen,
If you really need to keep up to date, maybe you should install everything using MacPorts[1]
There is an article[2] describing how to ‘sandbox’ Rails with MacPort in order to have multiple version of your pre-requisites installed. The update process after that is pretty much a simple command, ‘sudo port upgrade installed’.
You can do many more things with MacPorts, but you will be hard pressed to find documentation for it. Here[3] is the manual from when it was called DarwinPorts.
[2] http://blog.duncandavidson.com/2006/04/sandboxing_rail.html
[3] http://darwinports.opendarwin.org/docs/ch01s04.html
-christos