Sketchup is a pretty viable option, you can get a lot of detailed modelling done with it. I know some of the guys at massive black use it and they get shit like this done with it:
Link
I don't talk from experience but from talking to people in the industry, and 3d is just a little experiment for me. But for the big jobs at the big studios, its about specialisation, they want the BEST concept artists, not someone who can do a bit of both. Smaller Indy studios are likely to want people who can go both. You get recognised by being really good at something and that normally means specialisation.
So for me its about being damn good at just concept art. Although I assume its good to have 'knowledge' of the other stuff, like 3d/lvl design, because its an important factor in the concept art.
Thanks for the love too, got some more work coming up that I'll post. Sick painting Vespa.