How can I play WAV and/or MP3 files into a Skype conversation? I'd
prefer a solution that's less technically challenging that Virtual
Audio Cables (VAC), which I understand is capable of mangling all the
audio streams in the right fashion - I'm hoping for something a little
more "turnkey."

Yes, I have the solution for you as I have done this before and it is
actually quite simple!

What you do is call your home phone with Skype. The reason for this is
you can only use your Microphone or Play music not BOTH (from the
computer that is).

You should have the "computer" on the line and then yourself on the phone. 

Now, simply load your audio application (I use WinAmp) and you are
going to make one adjustment to your Windows Volume controls.

Click on the speaker icon beside your clock if its there or alternativly:

Start->Programs-Accessories->Entertainment->Volume Controls. 

1. Click on Options at the top then click Properties
2. Put a dot where it has "Recording". Make sure "Wave" is checked off below.
3. Put a checkmark inside "Wave" instead of "Mic".

It will now broadcast your winamp playback onto the call instead of
your microphone.

Hope this helps :)

You can do *both* but you need a special soundcard that can bridge
wave & mic. This is the way I do it! Quite effective.

Enjoy.