I do a lot of audio DSP programming, and can create your custom audio spectrum visualizer in about a week. The different display methods shouldn't pose a problem as I've done similar visualizations before (multi-band spectrum, wave, spectral, VU meters... ).
I haven't specifically worked with VLC's audio-stream, but as with all signals - it's easily pushed through a FFT transform and the signal converted into a visual representation.
I done this in past projects for several of my own media players, and can provide more info and screenshots if you require.
regards,
Michael