I'm currently running elementary OS Luna, which is based on Ubuntu 12.04. Can I upgrade my installation to have a Ubuntu 13.04 base, but still use elementary OS's desktop environment and applications? Would elementary OS's packages break because they expect the dependency versions in Ubuntu 12.04? Would I be better off installing 13.04, building elementary OS's packages from source, and then reconfiguring all my preferences for everything?
It might work. Then again, it might not. Upgrading a distribution is a risky process at the best of times, I would be very surprised if you did not run into trouble. A better question would be whether it is even worth attempting?
Upgrading just to have the latest version is rarely worth the effort. You should upgrade to fix security holes or to get new features that you need. The basic principle is if it ain't broke, don't fix it. So, if all you want to do is get a newer version of a specific piece of software, upgrade that, not your system.
In any case, what you are proposing means you basically want to replicate the work that the elementary OS devs are doing. Elementary is basically Ubuntu + Elementary stuff. You are suggesting that you should upgrade to a newer Ubuntu and then install the elementary packages. If that were as trivial as you seem to expect, there would be little point in releasing elementary as an OS.
However, one of the great features of Debian's package management system is that it deals with package dependencies for you. So, if you want to get a newer version of something, modify your
/etc/apt/sources.list (which presumably already contains the Ubuntu repositories) and make it point to a newer version of Ubuntu. You can then run
apt-get update to refresh your sources and have access to the newer versions:
sources.listfrom this (or similar)
deb http://archive.ubuntu.com/ubuntu/ precise main restricted
deb http://archive.ubuntu.com/ubuntu/ raring main restricted
sudo apt-get updateand then install a newer version of your favorite software,
sudo apt-get install vlc
Elementary OS also provides a bleeding edge repository (which you use at your own risk, it will not be as stable as the released version), you can find it here.
Finally, if for whatever reason you really really want to risk this and upgrade your distribution (I stress there is very little point in doing this) you can try. However, there is no guarantee that the newer versions of the various core libraries you will install will be compatible with the Elementary packages. You will almost certainly end up having to tweak various things and I would bet it would take you longer than doing a fresh install.