Firstly, both your photos and illustrations are amazing and I like them. And your 'hoto-manipulations', as well :) As for your question - I have feeling that is similar to yours: something in between, fifty/fifty. Given that images are done perfectly well.
7d + lenses: Canon EF-S 15-85mm/3.5-5.6 IS USM & EF 100mm/2.8 USM Mac...
I guess here in stock photography, any manipulation make sense. The target of your pictures are mostly professional graphic people and designers and they do not care the purity of the proces but suitability of the picture to fullfill their need.
Canon EOS 5D MarkII, canon EOS 5D, canon lenses 24-70, 100-400, 70-200
I prefer to realize photography, but in many cases I am attracted to those graphic elaborations that can transform and improve a photo in those aspects that could hardly be captured by the simple use of the camera. Your portfolio is fantastic! I have already noted it before.
I do a little of all three (illustrations, mix, photographs) but I am just a beginner. However, they seem to all sell equally so far. I guess its like Midou3 said, "suitability of the picture to fullfill the buyers need."
Nikon Equipment, Nikon Lenses, Professional Photo Software
Always an interesting question. There is a distinct difference. I am very old school professional photography and stick with it. I tried this illustration stuff but just got tired of basically messing with my work which sells very well as it is. However, as your work shows, the results of messing around with images pays off for some and the results are quite stunning. For me to do it now you'd have to glue me down in front of my computer.