Another point of view:
I'm not sure what you'd really gain from adding another analog oscillator. If you had independent outpus and CV inputs for each of the oscs on the Voyager, I could see how another analog oscillator might be useful (you could sync osc 1&2 and 3&4 together, for example). But you can't do that sort of thing... you can only mix in the 4th osc. Also, 3 Moog oscs fill up sonic space pretty well... I don't know that another one would add much to the thickness of the voyager.
That said, I've recently purchased a few oscillators to compliment my Voyager (and my FutureRetro XS). They're (gasp!) digital! There are some wild digital oscillators on the market out there, and they are really capable of some special results that you just can't get from a Voyager alone.
So far I have a Modcan 58B VCDO (
http://modcan.com/bseries/VCDO.html ), a Synthtech Morphing Terrarium (
http://www.synthtech.com/demo/e350/ ) and a Harvestman Piston Honda (
http://www.youtube.com/watch?v=UYJyXXs9_dA ). I'm planning on adding a Modcan B Miniwave as well.
Any one of these would open way more gateways from a sound-design standpoint than adding another analog oscillator.
I also see a modular in your future!