I'm really, really, really cautious about doing that. I need to feel really inspired to work on anything at all and I can't turn that on whenever I want, though that's the goal. I have a mountain of my own music that's been waiting 3 years for that motivation to turn back on and now that it's back, I've happily working away at it, while creating a stockpile of all new stuff to work on.
I know one thing is for certain, I won't take on anything singing lyrics/melodies someone else wrote. The part I get off on the most is hearing something in my head and making it happen, the performance part is often a means to an end within that. Whizzin's song is a great example; as I heard it, all the vocals were already 'there', I just fit words to what I heard and turned on a mic. But it's very much not the same thing when someone hands me the lyrics/melodies and they're 'there' already.