I think you can find the howto about X here:
http://www.droidforums.net/forum/droid-x-hacks/. I have a D1 so I am not 100% sure though.
If I were you, I definitely would look into rooting the phone. I am not crazy about themes, but there are some extremely practical benefits only available to rooted one. For one, nandroid allows you to backup the entire phone so you would get it as is when restoring the backup in the future. I don't think stock phone can run nandroid.
From there, you have the option to overclock the phone. If you are willing to spend the time, you can design and deploy your own themes. The snapshot I posted earlier was taken by drocap2, a root-user application.
The downside of rooting the phone include chances to screw it up in the rooting process (it still exists.), then followed by possibility of having a very time-consuming habit.
Enjoy your phone.