I simply wondered whether people thought it was worth learning to use the MSBuild syntax in order to customise the build process for a .net project, or whether it is really not
In a scenario such as yours, where you do not already have a build system, then yes, MSBuild is absolutely worth it. Not only can you use it for a variety of pre-build and post-build tasks (see Jicko Petiov's answer), but you can also integrate it nicely into a continuous integration environment (such as CruiseControl).
One scenario where it might not be worth it is when you already have an automated/scripted build system in place. For example, I myself haven't taken the time with MSBuild because I've been using NAnt for this task since before MSBuild existed ...